Basics first:
You get the ball launcher when you pick up the ball, or it is passed to you, in a Bombing Run? game. You regenerate health while you have it and cannot switch weapons. The primary fire throws the ball or passes to a locked teammate - the secondary fire locks on to a teammate.
Ok, while you have the launcher, always pass forward whenever possible, otherwise just run towards the enemy goal. Get people to translocate ahead of you. When near the goal, by all means go for a 7-point run through if you can, but don't dissmiss the three points you get for throwing the ball through the goal if you suspect you might be killed before reaching the goal - especially if your team is already winning.
If you find yourself in a one-on-one situation where you have the ball launcher, throw it to your opponent - he'll be forced to lower his weapon to take the ball, leaving you free to frag him while he works out what just happened.
If you find yourself cornered by enemies without anyone ahead of you to pass to, pass the ball backward if you can. Alternatively, throw it off the edge of a cliff or into an unreachable or instant-death area - this will reset the ball to the centre of the map, denying it to your opponents.