@Katrina96,
Not enough information to know right there -- kids roughhouse at the pool, and a lot of it I wouldn't discipline. Depends a lot on how old the little sister is, how upset she was, what the context was, etc.
I think it would have to be pretty egregious (harm or imminent harm) to jump to taking away a day of hockey (I think middle ground would be something like just making sure he understands he has to be more careful, and that you don't want it to happen again). But again I could see things going either way (mostly-harmless roughhousing that doesn't really warrant a response at all, or actually dangerous behavior, or somewhere in between).