The Unsettled Drill
Another lacrosse coaching technique is an alternative to regular 6v6. Separate your offense (Put them on the sidelines on one side of the field) and defense (Put them on the other side line). The head coach is with the offense, while the assistant coach, or defensive captain is with the defense. The coach says a number such as, "four" so that only the offense can here it. At the same time, the defensive coach says a number, "3" so only the defense can here it. 
When the whistle blows, both offense and defense sprint onto the field (each with their respective number of players), and they play unsettled, until the ball is cleared or goes in the goal. 

Once the play stops, the players go back to their respective sideline, and the drill starts over again. Note that if the defense or offense is vastly overwhelmed, just keep playing. 

This drill can look very disorganized, but it has some great key elements. It has conditioning, with the players sprinting onto the field each whistle. It has communication, the players must decide who is going out onto the field. And most importantly, it is a pretty fun drill.