a nick name bestowed upon somebody that has sucked so many dicks or presently has so many dicks in his/her mouth that they may as well be a package of hot dogs, hence ballpark. also you may call the person a particular stadium like fenway or yankee stadium.
Guy 1: Hey, how was your night last night with your girlfriend?
Guy 2: Awesome! Fucking Ballpark Franked her!
Guy 1: Wow, really?
Guy 2: AWWWWW YEAAAHHH