We had something similar happen with a daycare child. She tried to climb out of her pack and play and pulled her front tooth outward on the bar of the pack and play. It was sticking straight out! She did go to the emergency room because we were not willing to do what the nurse said to do over the phone. We were told to pop it back in place and that's all anyone could do. Dad took her and when he did, the doctors in the emergency room were also afraid to do it. So they brought in a pediatric dentist and he did it. That's all he did. He told us to make her go back to baby food for a month. We were to push the tooth up into place many times per day and hold it there as much as he would let us. It was hanging down way lower than the other tooth. He said it had about an 80% chance of turning black and falling out. He said if it did harden up and stay in it would still change colors. So we went through the next month of pushing it up and bit by bit by week 2-3 it didn't seem to be hanging so low. It never changed colors and eventually it did harden up. It sits a little crooked in it's slot. But the great thing is that it stayed in place to keep all the other teeth from coming in crooked. Oh yeah, and it never changed colors at all. In fact, you wouldn't even notice it is crooked unless you know what she did.
Your sons tooth may have a better chance since it's not hanging down. Her's was barely in there. It would have taken nothing to make it come out all the way. You should be really careful with your son and not allow him to do any rough housing so that he won't hit it again. Also, you should feed him soft foods. Hopefully he likes yogurt, oatmeal, apple sauce etc. Let him have a lot of milk shake like products like Ovaltine or better yet, Slim Fast. It won't hurt him at all and is filled with vitamins. He should not bite on anything hard until the tooth is hard in place again. If it does start to turn colors, get more loose and needs to come out, then yes he would need to see a dentist and get a metal placer put in. That way his teeth won't shift and become crooked so that he needs braces later.
Suzi