Douglas Harper's Etymology Dictionary
"thrash, strike repeatedly," c.1900 (v.), from beat (v.). Beat-up as an adjectival phrase meaning "worn-out" dates to 1946.
Wiktionary
(context slang English) Battered by time and usage; beaten up. alt. 1 (context transitive English) To give a severe beating to. 2 To attack suddenly; to alarm. 3 To cause by some other means, injuries comparable to the result of being beaten up. 4 (context reflexive English) To feel badly guilty and accuse oneself over something. ''Usually followed by over or about.'' 5 (context military WW2 air pilots' usage English) Repeatedly bomb a military target or targets. 6 To get something done, ''derived from the idea of beating for game'' 7 (context intransitive nautical English) To sail to windward using a series of alternate tacks across the wind. 8 To go diligently about in order to get helpers or participants in an enterprise. n. 1 A person who, or thing that, has been beaten up. 2 An act of beating up: 3 # (context UK military slang English) A raid. 4 # A beating; a hazing. 5 (context UK Australia New Zealand English) An artificially or disingenuously manufactured alarm or outcry, especially one agitated by or through the media. 6 (context forestry English) A tree planted later than others in a plantation. v
1 (context transitive English) To give a severe beating to. 2 To attack suddenly; to alarm. 3 To cause by some other means, injuries comparable to the result of being beaten up. 4 (context reflexive English) To feel badly guilty and accuse oneself over something. ''Usually followed by over or about.'' 5 (context military WW2 air pilots' usage English) Repeatedly bomb a military target or targets. 6 To get something done, ''derived from the idea of beating for game'' 7 (context intransitive nautical English) To sail to windward using a series of alternate tacks across the wind. 8 To go diligently about in order to get helpers or participants in an enterprise.