Green’s Dictionary of Slang

a general excl. go easy! stop it! be sensible!

1918		Referee (Sydney) 10 July 11/1: ‘Easy on, old mate,’ Sir Claude said tactfully, noticing the angry gleam in his friend's eyes, and the flush upon his face.
1941		Baker Popular Dict. Aus. Sl. 27: Easy on!, go easy! desist! be sensible!
1955		N. Pulliam I Travelled a Lonely Land (1957) 233/1: easy on! – take it easy, be careful.
1974		V.E. Smith Jones Men 26: Easy on the piece, man.