Learn English – How or why did “sock” come to mean “punch”

It might be of Wolof origin. Here is an excerpt from The African Substratum in American English (by Margaret Wade-Lewis - 1988):

sock. The colloquial verb to sock means 'to hit or strike forcefully,' 'to punch,' 'to deliver a blow' (American Heritage. 1976: 1226). Its probable origin is the Wolof verb /s 1 k/ , meaning 'to beat with a pestle,' 'to strike' especially with something.

_{Note: Wolof (/ˈwɒlɒf/) is a language of Senegal, the Gambia, and Mauritania, and the native language of the Wolof people.}

Moreover, the similar sounding verbs in English and Wolof are observed by the British linguist David Dalby in 1969 (from The Slavery Reader, Volume 1 By Gad J. Heuman, James Walvin):

The verb "sock," in the sense of "to strike," especially with something, has recently been popularized in the black American phrase "sock it to me" (with an obscene connotation), and is reminiscent of a similar-sounding verb in Wolof meaning "to beat with a pestle.

The Dictionary of Word Origins (by Joseph Twadell Shipley - 1945) has a different approach:

Sock, in the slang sense, to beat, is one of a series. When you urge a dog to sick 'im, the verb imitates the sound you make; a form of Seek him! (common Teut., AS. secan). One step stronger is to sock 'im ; the next stage, to soak 'im one!

Then, the same book includes the etymology of sick, soak, steep, sugar and stoop; and tries to make a connection:

If you are sick, the word is common Teut., AS. seoc. (Sickle is a diminutive, from L. secnla, from sccarc, to cut.) To soak, to steep, is fcom OE. socian, to suck in, a weak form of OE. sucan, whence Eng. suckj L. sh- gcrc, suet — , to suck; whence Eng. suction. A little one that sucks is a suckling; from this by backformation comes the verb, suckle. Sugar may have been influenced by L. sugere; it is win OFr. Sucre, from zuchrc, from LL. cuccarum, from Arab, sukkar. The verb to steep is from OE. steap, from OTeut. staupom, a vessel for water. The adjective steep is also from OE. steap, from OTeut. staup, stup; from this comes the OE. weak verb stupian, to lower, to bow, whence Eng. stoop. One will stoop to put on (or dodge) a sock.

_{Note: There might be typos in the excerpt. I copied and pasted the original text.}

OED, World wide words, The Routledge Dictionary of Historical Slang, Oxford Dictionary of Modern Slang and some other similar sources; all say unknown origin. However, OED has the earliest citation from 1699:

Sock, to Beat... I'll Sock ye, I'll Drub ye tightly.

_{B. E. · A new dictionary of the terms ancient and modern of the canting crew · 1st edition, 1699 (1 vol.)}