Green’s Dictionary of Slang

tar n.3

[fig. use of SE tar = essence, ‘daylights’]

In phrases

kick the tar out of (v.) (also batter..., beat..., knock..., lick..., pound..., scare..., whale…)

[20C+] (US) to beat someone up very badly.

tar out (v.) [i.e. to beat the tar out of]

[mid-19C–1900s] to punish, to beat.