Special weekend events, like pump day, limited paint games, newbie days and the like.
Secondly, since games of CTF always become kill the other team, make it more fun by adding in a benefit of capturing it. Say a bag of paint to the player who hangs it or a free refill or even a green fee for their next time out.
Like stated, good refs who know what they're doing go a long way, and find someone who has some EMT background to be at the field at all times, I've heard this will keep insurance down some.
Know me by name; Shepherd of Fire!