I believe that the J-toss
refers to the motion of the tossing hand (and arm). Renowned coach, Vic Braden, advocated this tossing motion back in the 70s and 80s. I learned it from his younger brother, Dan Braden
, in the late 70s.
The motion of the hand describes/simulates the letter J
. The hand starts extended out toward the net. It moves downward and inward (closer to the body). As the hand reaches its lowest point, it hooks back upward (and often slightly forward) -- thus making the letter J
. With the J-toss, the arm often lifted parallel to the baseline (or somewhat parallel).