This will come with time and will unlock as soon as you reach 10,000 paintballs. You more than likely will have this before you get halfway through all the tournaments. If for some reason this is the last trophy you need just go into an exhibition match. Set the mode to Elimination, rounds to best 1 of 1, time limit to 10 minutes and team size to 1 vs. 1. Go to bots and change ther skill to rookie. You will want to go into paint and change it to infinite. Now go to rules and set reinsertion to on (0 sec). You will want to make sure that you have a gun that has a high fire speed, The Angel A1 JoyFly is a good gun to use. Just start the game up and rapidly tap and to fire as many paintballs as you can in the time frame.