Holding nothing back. Usually refers to ending something.
The term comes from the hammer action on a gun. The hammerdropping on many pistols is what causes them to fire. If you "drop the hammer" on somebody, you go all out.
An idiomatic expression meaning roughly "to explode in a fit of rage and fury", it is derived from the action of a firearm hammer "dropping" -- or striking -- the firing pin which in turn impacts the round and causes the mini explosion that results in a bullet or other projectile being launched at a high velocity out of the end of a barrel.
The expression can be used in several different variations with the above definition: 1) ...part. in a draconian way 2) ...leaving a wake of destruction in its path 3) ...against a very specific target with precision; etc.
"I have a clear shot of the target. Requesting permission to engage."
"You have the green light. Drop the hammer on that motherfucker."
BANG. Bad guyfall down.
Poker terminology.
When someone raises early (usually pre-flop if playing Holdem) just to push other players around, and you just can't take that smug grin on his face, you re-raise a ridiculous amount and "drop the hammer." This most often occurs during a Testosterone Fight, and the object is to make the other player put his testosterone hose away and fold. Since it is pre-flop, this has nothing to do with the cards you have, just plain good ol' fashioned balls.
Sam: I call.
Ryan: I call.
Mike: I call.
Kevin: I call.
Marco: I call.
Matt: I call.
Dana: I call.
Devin: I call.
Dave: Well... I'll just double the blinds so I have even stacks... mwaahaahahaa...
Devin: Fuck that! I'm DROPPING THE HAMMER! All in, bitch!
Sam: Coooold bloooooded.....
Expression in poker when someone raises you just to push you around and be a tough guy, usually preflop in Holdem, and you turn around, whip out the testosterone hose, and re-raise a ridiculous amount.
Matt: I call.
Ryan: I call.
Marco: I call.
Sam: I call.
Devin: I call.
Dave: Actually, I'm just gonna raise that a little bit.. double the blind.
Devin: Fuck that shit bitch! I'm droppin' the hammer!