It depends on the assault. Simple assault may be manageable with a public defender if you are clearly taking a plea. But felony assault, domestic assault, or assault with a weapon can put you away for years. Those cases need a private lawyer who has the time to interview witnesses, get the 911 call, and pull the surveillance footage. Assault cases often come down to one person's word against another's. That is exactly the kind of case where a private lawyer's time and investigation make the difference.