Green’s Dictionary of Slang

tear into v.

1. (also tear in) to throw oneself enthusiastically into a task.

[UK]R. Tressell Ragged Trousered Philanthropists (1955) 217: It was therefore in the hope of being one of the favoured few that while inwardly cursing the rest for ‘tearing into it,’ everyone as a matter of self-preservation went and ‘tore into it’ themselves.
[US]Van Loan ‘The Extra Man’ in Buck Parvin 28: You tear in and save the lady.
[UK]‘Henry Green’ Living (1978) 254: ‘Yessir’ foreman said ‘they’re tearing into it.’.
[US]D. Runyon ‘Little Miss Marker’ in Runyon on Broadway (1954) 297: The little doll tears into it very enthusiastically, using both hands.
[NZ](con. 1940s) G. Slatter Gun in My Hand 92: Mugs up men. Get amongst it. Tear into the good stuff.
[UK]K. Bonfiglioli Don’t Point That Thing at Me (1991) 27: We all three [...] tore into an enormous fry-up.
[Aus]R.G. Barrett Mud Crab Boogie (2013) [ebook] Warren and Debbie were [...] pulling cones from a bong on the coffee table while they tore into about a gallon of vodka.
[UK]K. Sampson Powder 81: The Grams tore into their set with deranged energy.
[NZ] McGill Reed Dict. of N.Z. Sl.

2. to attack physically, or verbally.

[US]J. London Valley of the Moon (1914) 35: Hurray for the old lady! Look at her tearin’ into ’em!
[US]H.C. Witwer Classics in Sl. 28: He won’t rest ’til Hamlet has tore into said uncle and made him like it, for revenge.
[US]C.R. Shaw Jack-Roller 125: He tore into me for calling him ‘nigger.’.
[US]N. Algren Never Come Morning (1988) 55: The way you looked when you tore into Poor Charlie!
[Aus]D. Stivens Jimmy Brockett 277: Make it strong, brother. I don’t care how much ginger you put into it. Tear it into Regan.
[US]M. Spillane Return of the Hood 41: Penny tore into old Rudy Max and broke him up for not paying protection.
[UK]G.F. Newman You Flash Bastard 69: Every villain and piece of scum who ever got a living from crime can, whenever he’s nicked, tear into the most practical, hardest working copper.
[Aus]B. Humphries Traveller’s Tool 35: We were tearing into each other like a pair of blue-tongued lizards.
[UK]D. Jarman diary 29 Aug. Smiling in Slow Motion (2000) 208: They were venomously tearing into two pretty boys sitting across the restaurant.
[Ire]F. Mac Anna Cartoon City 40: He expected Lucy to tear into him. Instead he was pleasantly surprised when she came up and kissed him on the cheek.
[Scot]A. Parks April Dead 22: [B]lissfully unaware of what was going to happen to him in the morning [...] and Mary got torn into him properly.

In phrases

get tore in (v.)

(Scot.) to fight vigorously; to commit oneself wholeheartedly.

[UK]G.M. Fraser McAuslan in the Rough 11: Him an’ his mates, they wis inna Foreign Legion, inna fort [...] an’ the wogs wis gettin’ tore in.
[Scot]A. Parks Bloody January 74: They squeezed in at the bar between [...] couple of soldiers getting torn into it.