Green’s Dictionary of Slang

meanly, contemptibly, unpleasantly.

1894		Truth (Sydney) 11 Nov. 5/7: This was ‘playing it low down’ on the country with an Imperial vengeance.
1908		‘Doss Chiderdoss’ ‘The Hand-Shaking Peril’ Sporting Times 18 July 1/3: You’ve been playing it low down on me, / But we’ve shaken hands now, and are quits!
1918		Kia Ora Coo-ee 15 Aug. 17/1: After I’d been in Hospital for about three weeks, they treated me pretty low down, I thought – took me off ‘light diet’ and sent me into the ‘bull ring’ for meals.
1919		Wodehouse ‘Leave It to Jeeves’ in My Man Jeeves [ebook] It struck me that it was playing it a bit low-down on the poor chap, avoiding him like this.