also: come off · work up · climb to the backer
Leaving a block you are already on to go block somebody at the second level. Named separately from the combo because the timing of it is what decides whether the play works.
2 meanings, all below. Jump to the one you heard.
The departure half of a combo block. The lineman gets the down defender moving with his partner, then releases and works up to a linebacker.
It is a read rather than a count. What the lineman is waiting for is the down defender's weight committing to his partner, and what he is watching is the linebacker, because the point is to arrive where that linebacker is going rather than where he currently is.
come offveer releaseUsed more loosely, to climb is simply to get to the second level. A coach saying "climb" to an uncovered lineman is telling him to go find a linebacker, with no double team involved at all.
The two senses matter because they describe different difficulties. Climbing off a double team is a timing problem. Climbing from uncovered is a targeting problem, and the failure is a lineman arriving in the right area with nobody to block.
work up, get to the second levelcombo block