I can’t believe we haven’t covered this before, but I can’t find it: where does the expression “beat the tar out of someone” come from?  Is it nautical?  (I have temporarily lost access to the online OED, so I can’t check that, but it doesn’t seem to be in the first edition.)

OED online says “to beat (knock, etc.) the tar out of: to beat unmercifully, to reduce to a state of helplessness. Cf. SHIT n. 1g. U.S. slang.” 1st cite is from 1884 (National Police Gazette).  “Beat the shit out of” is first cited from 1966, but of course profanity in print tends to lag behind oral usage.

I suspect that “tar”, as a dark-colored semisolid, is euphemistic for “shit” in this expression.

"Knock the tar out of ...” coexisted with other expressions by 1890, of which the one with “stuffing” seemingly was a favorite. Farmer & Henley show “bottom”, “stuffing”, “lining”, “wadding”, “filling”, “inside”.

“Daylights” is old also. I’m not sure whether this referred originally to consciousness/senses or to internal organs or to something else.

“Hell”, etc. of course is also a perennial favorite, I suppose quite old, as is “Devil”.

“Knock the shit out of ...” can be found at G-Books as early as 1886.

Hypothesis 1: “Tar” refers to tar or tar-like substance with which some conventional item was stuffed way back when, thus “tar” = “stuffing”.

Hypothesis 2: “Tar” is euphemistic for “shit”.

Hypothesis 3: “Tar” (cf. “tarnation") is euphemistic for “Hell”.

Hypothesis 4: “Tar” somehow represents “daylights” or so (seems inchoate to me: suggested by Cassell’s slang dictionary).

Tar wasn’t used for stuffing, but it was widely used for waterproofing - tarpaulin (tarred canvas) of course; the rope rigging of ships; and such items as sailor’s hats and jackets. Prolonged foul weather at sea would eventually have beaten the tar out of these surfaces, leaving them soft and - unless they were re-tarred - permeable, i.e. unfit for their functions. That seems to me to be a perfectly plausible metaphor for beating someone up.

I find myself agreeing with Syntinen—“tar” doesn’t seem to me a very likely substitute for “shit,” and I wonder if the OED was suggesting it was or simply comparing the phrases’ form.

Tar on ships and elsewhere was used to stiffen fabric, rope or anything flexible as well as for waterproofing. To beat the tar out of someone could mean something as simple as a beating removing any protection, rendering the victim helpless to the slighest element of weather or human attack. Is this far-fetched?