What Karl said. If your concrete base is large enough, offset the post slightly and install four new anchors. These would do nicely, however,they absolutely don't need to be placed near the edge of the concrete or they'll blow out the side. What does the concrete base look like?

anchor at Lowe's (these are also used to mount car lifts...they're pretty darn strong).



You probably could weld the j-bolt back together by tinking out a little concrete around it to expose some of it, welding, and then filling with a little concrete patch. It's strength may be questionable but if it's in the front, nearest the backboard side of the post, I wouldn't be too concerned about it unless there was something behind it that would be damaged should it fall back.