As in they turn rabid and start attacking people? Over under training is a proven method for increasing speed.
yes but only after you have acquired good technique and Basic Fitness. I would first do a technique program like wasserman's stuff as well as some Basic conditioning like bands. later if the Progress stalls you can use weighted balls. I think Kyle Boddy said he doesn't work with athletes before HS Age.
I definitely would not do weighted balls with a Player with bad/pushy throwing mechanics.