Are you trying to make it believable, or are you trying to make it unbelievable? It is a fantasy, after all.
The whole notion of throwing weapons is fairly unbelievable. We know that some warriors of old carried them (from shuriken to throwing knives to throwing axes/hatchets), but the reality is that precision throwing weapons have never been more than a circus side-show, never a real combat doctrine. Even notoriously inaccurate DnD rules get this one right, in that they don't allow for precision throws of weapons beyond 10 feet--and even that is generous. The investment in time and effort it takes to get a person to the point where he can throw a weapon accurately beyond six feet (two arms' reach, or the reach of an arm and a sword, the nominal limit of what we gamers call "melee" combat, i.e. hitting people with held objects) is simply prohibitive, not worth it when weighed against the nonexistent benefit. If you want soldiers or warriors who can affect an individual targeted enemy beyond melee range, you're much better off teaching them to use first a spear (held, not thrown; get your reach the easiest way possible, by just holding a longer weapon), then a bow if a spear still isn't long enough. They can become lethally proficient much more quickly. Second, a bow also produces far superior penetration. It is always penetration that kills, in combat. (The hacking sword frightens; the thrusting sword kills.) A thrown weapon is going the be more annoying than deadly, especially to a target wearing, y'know, clothes. Even light armor will thwart anything but a perfect throw of a very sharp weapon. Third, a bow allows more ammunition per weight. A warrior's load is already heavy enough. Why would I add ounces in the form of knives or shuriken which are single-use--literally, which I am going to throw away on the battlefield--and which the enemy's buddies can then pick up and throw back at me or use to stab me if they do break through my melee defense? Thus, the vast majority of even elite warriors went into battle with polearms and bows (with swords as fall-back weapons, similar to a modern soldier carrying a pistol to complement his rifle). I've never looked into it, but I suspect even the famously purpose-built shuriken was never actually regarded as a killing weapon outside of legend. Ancient warriors were scientists of killing. They thought in the language of killing, as we do today. A warrior looks at a throwing star, and those short tines, offering only a couple of inches of expected penetration, tell him as clearly as if it had been shouted that this thing is not designed to kill a man but for some other purpose. To the extent that there were real ninja or others running around with such tools, I'll lay money they used shuriken to stagger or distract a lightly-armored attacker as they fled or pressed an attack into melee range.
The above all speaks to a specific concept, which is the "precision thrower" of legend. The idea of throwing a sharp weapon at a specific guy and hitting him in such a way that he dies from the wound. This is an extension of the concept of precision ranged attacks generally, the idea that one fighter can target another single, individual fighter at beyond melee distance and reach him with some kind of missile, with enough precision (and force!) that he dies from the wound. The truth is that any precision ranged attacking, even with bows, crossbows, and guns, was rare prior to the advent of the rifled barrel and limited to a distance of (again, DnD surprises us with its accuracy) probably about thirty feet, give or take. Beyond that, most archers and musketeers were not going to be able reliably to hit the vital zone of a single, selected enemy--especially a moving, armored enemy in the heat of combat. And inside a distance of thirty feet, a normal archer or musketeer is going to manage one shot and then get overrun, so he will probably drop his ranged weapon and go to melee--or run away--rather than try to Legolas it out with his foes. So this means even the dedicated, skilled archer ends up performing relatively little, if any, precision shooting, at any distance. Beyond 30 feet he can't, and within 30 feet it's too late. (Again, 30 feet here is just a rough gauge of the outside distance at which a trained archer could reliably target and hit the vital zone of an enemy in combat.) Only with a rifled firearm do I actually begin to consider ranged weapons as precision, targeted weapons at any distance. With a rifle, suddenly, beyond 30 feet I still have plenty of accuracy, and within 30 feet I have a combination of per-round lethality and rate of fire that makes my pistol or carbine still far more deadly, a far more efficient killing machine, than your sword or spear.
The actual shape of ranged combat, in the vast majority of instances of its use prior to the rifle, was (as you have probably guessed or already knew) the formation volley. Early European warfighters opened with volleys of thrown hatchets or hunting javelins (atl-atls?). (There was one particular small axe design with an oddly bent handle, of which I forget the name, which one recreator theorized, after some experimentation, was designed thus so that if it missed a target, it would bounce wildly off the ground, allowing it to hopefully score a telling leg hit in a dense collection of enemies.) Roman legionnaires would open with two volleys of pila. Medieval armies would open with volleys of arrows. And later armies would fire muskets and cannon in volleys. Nothing particularly targeted, as a general rule. Just numbers against numbers, forcing attrition as the two sides close.
BUT...
This is a fantasy. We have legends of warriors killing with targeted, precision throwing for a reason. A few did develop those skills to such an extent that they could at least be demonstrated on a static target board and used as a means of off-field competition--especially among ancient warriors, prior to the advent of the professional army and the phalanx (in all its various forms and names across various cultures; every culture which is serious about war eventually invents a phalanx concept). An ancient warrior who could hit a melon with his axe or knife at twenty feet could probably at least claim that he was
more likely to land a lethal hit at greater distances during the opening volley, or
in extremis during the melee mix-up when he might use his last remaining axe or javelin to at least disable one of several oncoming rushers before engaging the rest with his held weapons. These skills and demonstrations, and the naturally heightened records of great warriors of ancient times, mean that the idea of the precision knife throw, precision killing shuriken, precision axe and javelin, are a natural feature of warrior legend, then and to this day. Fantasy, remember, is not a reflection of historical record but legendary record. If you play a fantasy, you're not supposed to be playing in the world of a medieval person but in the
stories, the heroic epics, which medieval people recounted by firelight and in ritual.* Your hero is not a real person, he is a character of legend. Therefore, he should do things that legendary characters do, and one of them might be throwing daggers into people's throats in the middle of a fight, because that's awesome and it illustrates some cardinal virtue of the storyteller's culture. If he is doing that, then he's probably repurposing some throwing weapon that is already common to his era as a volleying or harrying weapon, well known to the storytellers who are telling his legend to their grandchildren at bed time. Is his culture more primitive? Then it's probably a small axe. More Classical? Maybe a short spear. (I personally love the idea of the javelin, and most of my DnD strength-melee characters carry a few and chuck them at mooks for style points.) Is his culture capable of producing light, balanced, symmetrical blades? Then throwing knives--or, if it's aesthetically appropriate--throwing stars.
Could he use a couple of these to help him in a 5-on-1 fight? Abso-frickin'-lutely. You have this underlying question: "How would a guy take on five assailants at once and win?" You want a model for this accomplishment. Well, if you're writing the next Jack Reacher clone, then you and I can talk about how that might really look, what we might really do to survive that encounter and come out on top. Let's look in your area for a good martial arts school that might let you learn these skills and experiment with some many-on-one engagements. But if you're writing heroic fantasy, and you want to know how a hero would handle it, then what you want to do is read the Illiad, the Odyssey, Beowful, and so on, and imagine how these guys would manage five oncoming mooks, and then let your imagination put your own spin on it.
* Remember, "heroic" here does not mean "the guy was a hero" like we mean hero, like he saved a lot of people. "Heroic" in the literary context has a different meaning. It refers to the heightened aspect of a legendary figure, usually a warrior of some kind, who is used in a culture's stories to exemplify and illustrate that culture's prime virtues, such as strength, cleverness, perseverance, loyalty to king or country, faith in the gods, etc. The trials of the hero are a way to illustrate for children the virtues which the community values and wishes them to emulate and preserve.
This is what Tolkien got right, and which so many fantasy authors since have missed, which is why their work somehow always seem to fall short of his: He did not write the history of Middle Earth; he wrote the stories of Middle Earth. His expertise was in the ancient heroic epics and legends, and his academic thesis was that the fundamentally unrealistic fantasies which the ancient cultures produced as their "histories" were not just illegitimate product of primitive minds, but rather were creations with a purpose--though a purpose different from what we use history for today. Specifically, he was one of the earliest well-known scholars to recognize the cultural purpose and significance not just of the hero, as I've defined it here, but also of the legendary monster. He wrote his fantasies of Middle Earth in that vein, from the perspective that he was recording not what "actually happened" but rather what would have been retold in those cultures' oral and written traditions. The result is a story that feels, authentically, like it fits in with the Beowulfs and Illiads and Tains, rather than just feels like an unrealistic fake history.
You might even say that all the people who feel like later fantasy doesn't quite match up to Tolkien's because nobody's world-building is quite as good as his have missed the fundamental truth: Tolkien never did any worldbuilding. Not a whit. "World-building," as modern fantasy authors/Tolken-emulators try to do it, is all about making a more believably complex, detailed, sprawling world--usually (tragically) beginning with a map. Tolkein didn't begin with a map. He began with a hole in the ground and an invented word, "hobbit." He never concerned himself with what the truth of the fantasy world actually would be, but skipped history and began his writing at the point of legend, because he knew that the literal, historical truth was not what was important to the ancient people who created legends. What was important to them was to preserve cultural qualities, specifically cultural virtues, encapsulated in the form of heroes, their trials, and their monstrous foes.
