means A large bag of coarse fabric for holding goods; as a verb, to dismiss someone from a job, to plunder a captured city, or to tackle a quarterback behind the line.

from The 'bag' sense is ancient and well-travelled: Old English 'sacc,' from Latin 'saccus,' itself borrowed from Greek 'sakkos,' which traces back to a Semitic source (compare Hebrew 'saq') — the same root that gives us 'sackcloth.' The 'plunder a city' meaning likely comes from the Italian phrase 'mettere a sacco,' literally 'put into a bag,' i.e. carrying off the loot. The slang 'to get the sack' (be fired) is often told as a workman literally being handed back his bag of tools as he's let go — a story that may well be true, dating to roughly the 19th century. The football sense is a modern American extension, evoking a quarterback being 'bagged.'