For one thing they speculated about their clients mental state on national television. The mere fact they held a news conference to announce their departure was an ethical breech.
The attorneys speculated about Zimmerman’s current mental state, based on his behavior in refusing to communicate with them. They did not speculate about his mental state at the time he shot Martin. There is no ethical violation in holding a press conference for what has been made into the biggest legal media story of the moment.
How about Martin’s attorney threatening the special prosecutor with “pandemonium,” i.e., riots, if she doesn’t file charges? In a media interview for a foreign news outlet, no less.