meaning of "tried leg-breaking" and "proved deficient"

[kjc0123]

What is the "tried leg-breaking" and "proved deficient" in the following sentences?

 

Forrest started a tale, this one involving a shoving match in a hospital emergency room, and Ray began to drift. His brother had also worked as a bouncer in a strip bar, a calling that was short-lived when he was beaten up twice in one night. He'd spent one full year touring Mexico on a new Harley-Davidson; the trip's funding had never been clear. He had tried leg-breaking for a Memphis loan shark, but again proved deficient when it came to violence. 

[Ouisch]

A loan shark is someone who loans out money at ridiculous interest rates, and usually with unrealistic payback deadlines.  Usually they hire thugs to "enforce" their payment deadlines.  Therefore, the man in your above mentioned scenario was an enforcer for a loan shark for a while, and actually physically broke the bones of people who defaulted on their payments.  However, he really didn't have the stomach for the job, so he quit, which is why he proved deficient.  He just didn't have the heart to be violent with people.