Recently went paintballing for a Friend's Stag do and decided to create these as a Souvenir for him to remember the painful experience :D
Pause the print at 55 - 60% and drop the paintball in so the bot can build around it. If you have a cooling fan, switch it on at this point also
Don't print with Supports as you'll have a hard time getting the support out without bursting the paintball.
Finally, I printed this with PLA. Not sure if it will work with ABS cause it uses much higher temperatures which could melt the paintball - and you don't want paint all over your printer and nozzle!