The basic scenario is that our character being shot at (Who is a five foot tall anthropomorphised squirrel, incidentally) has discovered the merchant caravan camp he's meant to be guarding is under attack, whipped about eight feet up a tree and is firing arrows at the melee below. And it's a big melee, with a huge range of weaponry being employed, but he's just out of range of the close combat stuff, and presumably his own guys aren't going to be shooting at him, but there's a lot of fires and the odd explosion as various kegs of gunpowder or crates of ammunition etcetera get blown up. And I want him to get hurt, in a very specific way. It's got to put him out of the fight pretty sharpish, and be potentially fatal (The main character has to believe he could be dead) but he luckily manages to survive. Bonus points if it means his chances of being a functioning archer again are slim.
I've originally written it so that a stray bullet skims the side of his face, clipping his nose, opening up his eye and then riccocheting off his temple. This manages to ruin his eyesight, knock him out, and even gives him a rather dashing scar for when our main character meets him again. But after searching through lots and lots of pictures of squirrels I'm just not at all sure whether or not it could hit his eye without hitting his brain as well, and surviving that is even more unlikely.
The ideal weapon in question being utilised by the enemy is roughly similar to an 18th century musket, and as such is wildly inaccurate. I'm fully aware that, given that the person being shot at is about five feet tall, heavily camouflaged and sitting in a tree in the middle of a pretty extensive attack on a merchant caravan camp in woodland at night with all the smoke and fire and other nastiness of attacking a campsite when there's kegs of gunpowder and stuff are exploding, if the person holding the musket was actually trying to hit him, he wouldn't have a chocolate teapot's chance in hell. That's okay. It's a completely random, stray bullet.
The good guys (That is, the side our squirrel friend is fighting on) are, on the other hand, utilising everything from bows and arrows to early 19th century rifles, although both are quite rare. Slings are good, although I don't think they'd do enough damage for my liking, and there's a fair smattering of flint- and matchlock pistols, so given the confusion of battle it could easily be friendly fire. Shrapnel from an explosion is also an option. Let your imagination run wild and lets see if we can't put the poor damn squirrel out of his misery (In a short term sense, of course).
Edit: Musket shot to the head is out on account of I don't want to crush his skull like an eggshell. Splinters to the eye is sounding good - after all, he's in a tree. Another thought has occurred to me (Actually, it occurred to my mother, but she readily admits she knows nothing about weaponry) - if the range is alright, which I think it is, how's a shot to the shoulder? Perhaps a broken collarbone that never heals quite right? Would he have a chance with that kind of a missile or would it inflict too much damage for him to survive?