What you did was steal/stealing

#1

onizoWhat you did was stealing

This is wrong.
Note: You can't have the -ing form in this kind of construction unless you have "doing" in the first part.

What you were doing was stealing is OK.

CJ

CJ, could you explain your reasoning?

I''d say parallelism applies.

What you did was steal...

What you were doing was stealing...

deadrat CJ, could you explain your reasoning?

Then, do you disagree?

Nobody has mentioned about #2. Is it just completly wrong?

Thank you everyone, by the way.

onizo, #2 is wrong. The article "a" is looking for a noun for theft. Steal is a verb; the verbal noun form is "stealing" or "to steal," neither of which take a article.

Note that "a steal" is American slang for a bargain, which only makes things worse in the sentence.

Rover_KE, maybe it's just me, but the bare infinitive form "What you did was [to] steal" sounds OK.

onizoNobody has mentioned about #2. Is it just completly wrong?

Yes. The word 'a' makes it wrong.

Thank you.

This definition on learner's dictionry, it says,

2 steal /'sti?l/ noun

a baseball : the act of stealing a base

• 
  He has 40 steals this season.
  

b sports : the act of taking the ball, puck, etc., from another player

• 
  a nifty steal by the defender
  
  ----------
  
  
  Based on this exa

deadrat CJ, could you explain your reasoning?

Look up "pseudo-clefts with do" in Introduction to the Grammar of English by Rodney Huddleston.

The same information contained in that book is also found at .

CJ

onizoWhat you did wasn't even half a steal this season. (To baseball player)

No, baseball doesn't work like that. It's either a stolen base (informal "a steal"), or it isn't. You can't have "half a steal".

What he did could not be counted as a steal, because he was tagged out at 2nd base.