There are a few different definitions of a clown. I'll try to explain it to give you the best understanding.
Firstly, every team has a team leader. This is the player (not counting the coach or any players who used to be the coach) with the highest leadership in your team. If you have two or more players with the same level of leadership, then you won't know which one is the team leader as it depends on how high they are in that level (which is something you can't see).
Now, the team leader influences your Team Spirit. The way he does this is depending on his agreeability. The levels of agreeability are:
popular
sympathetic
pleasant
controversial
nasty
Pleasant is the middle point where he won't have any impact on your Team Spirit at all. If he's sympathetic or, better yet, popular, then he will help your Team Spirit rise back to composed faster after you've MOTS'd, and slow the fall back to composed if you get it above that. However, if he's controversial or nasty he will slow the rise or speed the fall to composed.
Hence, the term 'clown' has come to be used when talking about a solid leadership with popular agreeability, which are the top levels you can hope for . Actually there is one beloved team member in the Hattrick world which is even above popular, but he doesn't have any leadership so he doesn't actually do anything. According to the story, he was created when the Hattrick Developers were at a party and somebody pulled an otherwise crap youth pull. They decided to have some fun and changed him to a beloved team member. :lol:
However the coach's leadership has a bigger influence than a clown. If your coach only has poor or below leadership, then a clown probably won't be able to help you keep the TS at above composed for the full week between games, although it will still help you a little to rise back to composed after you've MOTS'd.