Wrong HammerGrab defination. Only 3rd grab is real HammerGrab. About 1st grab, i can't remember the name of that kind of grab, but that is not HammerGrab. 2nd grab is GG2FG.
Real defination of HammerGrab is this. After CJ get some air, not on the ground, CJ throw your moto away toward the floor or ground when he is near the ground. CJ stepping on the ground, your moto crash on the ground and bounce to the air. Then, grab it.
For example
Slim's grab in his TMS audition with BoBsaget.
Sucker's grab in "Come From"
BigSmoke's grab in this tutorial section.
KillerK's HammerGrab1,2
and others.
HammerGrab is named like that because it looks like smashing with hammer to throw moto away.
If you follow the steps above but grab it side of the moto, not front of, you can call it HammerGrab also.