Did not 'banjo' used to be a term for giving someone a beating. The last verse of Barney Rush's 'The Crack was 90 in the Isle of Man':

The Isle of Man woman fancied Whack; Your man stood there till his mates
came back
Whack! they all whacked into Whack, and Whack was whacked out on his back.
The police force arrived as well, Banjoed a couple of them as well,
Landed up in the Douglas jail, until the Dublin boat did sail,
Deported every man, The Crack was Ninety in the Isle of Man.