"put the hammer down" - trucker term, meaning to go full speed, my guess is this particular term is a reference to the gear shift being the hammer, though I couldn't tell you how precisely.

"bring down the hammer" - to obliterate or defeat someone/something utterly

H.A.M.M.E.R. - acronym for a secret agency meant to be a replacement for S.H.I.E.L.D. in the Marvel Comics during one particular story arc, turned out to be a supervillian doing supervillainy things

M.C. Hammer - hiphop artist, mentioned by someone else in another comment.

"hammer away" - to stubbornly and aggressively work on a project/problem int he hopes of figuring out what's holding you back along the way.

that's all I got.