Rammer Jammer Yellow Hammer is a line from a cheer, typically played when the Crimson Tide has put a game away. Specifically the Rammer Jammer was an old campus magazine at Alabama, and the yellowhammer is the state bird of Alabama. They are juxtaposed in the cheer primarily because they are among a very few words that rhyme (approximately) with Alabama. If Alabama has beaten, say, the Tigers, then fans will stand and sing:
We just beat the hell outta you!
Rammer Jammer Yellowhammer
Give 'em hell Alabama