The setting is modern day (or thereabouts) in Sometown USA (exact details are unknown at the moment, but it might just simply be random j. town), and the fight takes place at an amusement park in a restricted area. Possibly even close to one of the roller coasters (naughty kids, yes) if that would help cause the effect I'm looking for (an unintentional kick to the head from a rider on the roller coaster, perhaps? Though that seems like it'd be closer to being lethal than what I'm going for). The other boy in the fight is a few years older (8-10 ish) and is fighting exceptionally dirty and is actively trying to seriously harm the character who goes deaf.
I tried searching google for "how much damage does it take to go deaf" and "hearing impairment caused by physical trauma" and similar search terms, but results don't seem to be giving me quite what I want, if even close to it. I've never possessed very good google fu, though, and I'm not entirely sure how best to phrase it, so it's entirely possible the answer is out there and easily findable, but I'm just asking the wrong question.
I also looked up deafness on wikipedia, but again it didn't seem to quite have the right info.
Any help would be most appreciated! It's a rather defining characteristic of the boy when he's older so I'd like to make sure I get it absolutely right.
Edit: Thanks for the assist! I was pretty sure I was right, but I didn't know it was -that- easy! Guess the scene'll be easier to write than expected.