Please be aware that most host parents were themselves younger people at one time in their lives.
If you want to self pleasure yourself I am confident that if you are a baseball player you are most likely a male. Most males still continue to masturbate; even when they are in sexually active marriages. It was, and always continue to be fun.
Now regarding any evidence you may be worried about. Please remember that you can use the bathroom shower to exercise your right to self pleasure and the sperm/semen goes down the drain. Should you have the option of working out a batch of sperm/semen between the sheets may I suggest that you learn now how the laundry equipment works. If you are in a host home they will be impressed when you volunteer to keep your own clothes clean in addition to the towels and bed linen. You will be considered a keeper. They may even let you come back next year.
Enjoy the opportunity that this program allows. You will meet new people and also have the chance to mature yourself.
Heck, if the Host Parents have a Garden/Lawn, you could even volunteer to help with the maintenance/grooming.
Enjoy the opportunity and become a part of the solution rather than be a part of the problem.
I wish you well. Play Ball and enjoy the opportunities.
Just think, the seven in the house have to be responsible for their own food. You will be the envy of you peers.