Green’s Dictionary of Slang

1. to start, to begin, e.g. hop into the grub, to start eating, often used as an invitation or imper.

1939		K. Tennant Foveaux 316: That’s all you ever will do if you don’t hop in and start before it’s too late.
1946		F.J. Hardy ‘The Load of Wood’ in Man From Clinkapella 11: Hop into it, and stop moaning.
1951		D. Stivens Jimmy Brockett 230: Hop into Downing, fellow, but don’t forget my other ideas.
1992		M. Coleman Fatty 282: ‘I was getting up at seven in the morning that hungry I could eat a horse and hopping into this soup’.

2. to fight, to attack.

1946		A. Marshall ‘Bushman’ in Tell Us About the Turkey, Jo 99: Hop into him, Bushman. Rip him wide open.
1951		D. Stivens Jimmy Brockett 62: I’d have hopped into them for two pins, but I had a lady with me.
2003		McGill Reed Dict. of N.Z. Sl. 105: hop into Vigorous attack on person or thing such as a job. ANZ late C19.