The act of using four of one's fingers to administer a handjob. The hand is not in the normal jacking off position, but rather the giver of the handjob comes from above and wraps all four fingers around the penis of the recipient. The position and movement of the fingers looks somewhat simliar to the movement of a jellyfish's tentacles, a lobster's claws, or how you would hold a baseball when pitching a four seam fastball. Invented by Elise, made popular by Muffin and Wills.
Elise gave Jack the four seam fastball, and Jack had to correct and show her the real way to do it.
This move is done after engaging in doggystyle secks. The man ejaculates into the woman's vagina. He then holds his hand like a cup underneath the semen (Jellyfish) filled vagina. With his other hand he grabs the woman's side and begins to tickle her. If done correctly it will cause a muscle contraction that forces the semen from the vagina into the cupped hand. When the woman turns to look back to see what is going on, that is when the male siezes the opportunity and hits her right in between the eyes with a Jellyfish Fastball.
Post intercourse, the man ejaculates into his hand, then winds up the Suicidal Semen Fastball firing it at his partner as fast and hard as he can, flinging the semen all across his partner's body.
" My boyfriend launched his SuicidalSemen Fastball at me, plastering semen all across my face. There were no survivors."