The details below are from the FAQ. I don't exploit the bug but there are many that have (or do).
1. What is team chemistry?
Team chemistry is the indicator how well the player is “gelled” with his team. Anything lower than 5 stars (meaning team chemistry 20), and the players performance is impaired. With team chemistry 1 (a newly bought or pulled player has a team chemistry of 1) a player plays about 30% worse. Each game the player plays ads 1 to the team chemistry. Players that are experienced can get 2 team chemistry points each game they play. Each point of team chemistry reduces the negative performance by 1.5%.

I tried it with one of my players, and personally I think that it is a visual glitch, and doesn't actually put chemistry up to 5*.

I'm wondering as well, why do you think ist is just a Visual Illusion?
It appears that it really works.

SrednaD wrote: Ebsmurdoc wrote: I'm wondering as well, why do you think ist is just a Visual Illusion? It appears that it really works. Me too... If it is a visual bug, all kickers should be treated badly on all teams... Or at least be in limbo if the other guys like them or not since TC is 5 star and everyone is smiling to you... or are they laughing at you... hmmmm ....

My kicker today, Milton Coates, did not get anything for team chemistry and he played kicker and punter. It was his first game playing and he is actually going to be my future kicker/punter, so I wasn't trying to take advantage of the alleged bug. However, in some thread back I was asked to prove that the bug doesn't work for my team and so I am mentioning it as proof that there is no bug, at least not for my team

Gatr22 wrote: SrednaD wrote: Ebsmurdoc wrote: I'm wondering as well, why do you think ist is just a Visual Illusion? It appears that it really works. Me too... If it is a visual bug, all kickers should be treated badly on all teams... Or at least be in limbo if the other guys like them or not since TC is 5 star and everyone is smiling to you... or are they laughing at you... hmmmm .... My kicker today, Milton Coates, did not get anything for team chemistry and he played kicker and punter. It was his first game playing and he is actually going to be my future kicker/punter, so I wasn't trying to take advantage of the alleged bug. However, in some thread back I was asked to prove that the bug doesn't work for my team and so I am mentioning it as proof that there is no bug, at least not for my team

As a matter of fact, this Bug does exist!
But it only appears if the player is only used as a kicker.