14 y.o. boy hit in side of head with a dodgeball. complained of headache, but it got better and was running and playing normally. brain damage likely?

Not likely: I would not expect a foam dodgeball to cause brain damage. If he has had a concussion it should be apparent and he should show some signs of impaired thinking or memory and pain. Usually following head trauma we watch for a significant change in personality or demeanor in the next 24 hours. If he has to change in his mood or an increase in pain then see the emergency room.