Dr Gil (definitely not a doctor) guesses torn meniscus, young enough for a repair, out 6-8 weeks (longer than the 4-6 for a chop & go, but better in the long run). It looked like he jammed it a bit on first base and it looked like something was catching in there. When he was being eval'd by the trainer, he could put weight on it (probably not ACL), and could run a bit, but then something caused him to pull up again. Hopefully I'm wrong and he just have to stay off it for a couple of days, but it didn't look very good.