There are some suggestions:
1. You can be proud of it - it's perfectly normal!
2. If seated, cross your legs.
3. Not to worry, it will eventually go away on its own.
4. Change your thoughts to something non-sexual.
5. Realize that you have sexual needs that are not being met and do something about it, e.g., masturbate in private or find someone who will help you meet your sexual needs in a healthy way.

Participating in active sports sometimes is a good way to deal with unmet sexual needs because it is a physical outlet.