Middle finger across 2-seam pointer and ring on side lile forkball when throw flick wrist down
a variation forkball is all.
Actually, that's a 3-finger changeup. Although not far off from a forkball. http://pitchingprofessor.com/Xchange_of_pace.html
I throw it with my fingers the 2-seams and it goes faster then a changeup