Unloving wild cat of mine?

My cat was the same way;; I rescued him from a pet store of all places. He was only 4 weeks, covered in fleas and sores, had the runs, and wasnt eating hard food;; cats love the outdoors and naturally want to go out to explore, I tried keeping mine in as well for I was scared he would get hurt by an animal or vehicle and even another person. He has random moments where his eyes get really big and he bites and doesn't let go. Perhaps taking him outside, maybe on a leash or in a playpen type setup wouldn't be a bad idea-- as for the attacking, he may very well be playing, he just doesn't grasp that hes hurting you while doing so. Give him treats when he does good and punish him (not like you would a dog obv) when he does bad.