Green’s Dictionary of Slang

peg n.2

[early 17C–19C]

1. a blow, esp. a straight-armed jab; thus peg in the daylight, a blow in the eye; peg in the victualling office, a blow in the stomach; peg in the haltering place, a blow under the ear.

2. in fig. use, a metaphorical blow, a verbal attack.