Defined as a field goal in basketball in which the shot follows a "loopy" trajectory, characerized by a high arc and punctuated by the incidence of the ball hitting the rim or the backboard in a fashion which is seen as lucky or heavily reliant on chance. The term plopper is derived from the fact that the ball "plops" in, meaning it drops into the basket in an unconventional way. Al Horford regularly relies on looping ploppers.
"Al Horford with a looping plopper. See Chuck, he's been doing that all season long"