When the middle finger and/or other fingers are inserted into the vagina and the thumb is used to stimulate the clitoris. Requires impressive dexterity, and if mastered leaves the other arm free to stimulate other body areas.
"I finally figured out how to bowlingball, so now I can finger a chick, and rub her tits!"
"Dude, my fingers are locking up from bowlingballing for so long!"
"Mike, you can't move your thumb fast enough to bowlingball me, just use your other hand."