getting him interested again...

a few weeks ago i uesd a chuck it stick to throw a tennis ball for harvey but unfortunately it hit him in the eye and he freaked now everytime i throw toys or roll anything outside even his favourites he won't chase it, just stands or chases it but doesn't pick it up and its a waste of time so is there anyway i can gain his trust or interest in the toys again. He's fine inside chases all his toys but i've resorted to throwing treats to get him to run outside and even if i give him a treat for getting his toys it on lasts about 2 throws, i used to be able to throw the ball non stop for about 20 mins and he came back each time and sometimes got a treat.