In the hospital he noticed how RK ill treated his daughter and how she was tortured by RK.
The only thing going on in his mind was that his daughter is suffering and he cant do anything abt it as he is on the hospital bed HELPLESS!!!
As soon as he recovered he had 2 options...
a) RK had make him sign the stamp paper saying that he will repay the amount RK gave MB to save shammu and free his daughter
b) Kill RK to free his daughter from RK.
And now we try to understand what option was more feasible.,..
a) It would take a long time for Malik to repay 40 lac rupees. He was not in the best of his health. He could not perform some deadly stunts in his ill heath to get money. Plus 40 lac is nt a small sum. He would have to perform stunts for lots of movies to make so much of money. That means it would take time if he went for this option.
b) This option meant take a gun from a pal and then shoot RK and kill him.
Out of both the options Shammu went for that option which was quick enough to resuce his daughter from RK.
PS: I am not saying that what shammu did was right ot wrong...I am just trying to understand his reasons to select option b to save his daughter...😳😳