Matt Steele teaches the Gangster Grip, Modified Gangster Grip and Super Modified Gangster Grip.
Jon Davis, a Marine Corps weapons instructor, posted a long article on Quora in which he suggested that gangsters hold their gun sideways due to the mistaken belief that you can aim faster that way …
I am a former Marine Corps marksmanship instructor. I specialized in pistols and have fired these weapons thousands of times. That said, the thought has crossed my mind. The answer didn’t come to me until another coach (from the “hood”) gave me a good reason why this technique would be used. In practice it actually does utilize one very important sighting practice, but fails overall. This is a good idea in theory, but fails miserably in the actual execution.
My theory is that gangsters shoot poorly on purpose. They need to be seen to be dangerous to both their comrades and to their enemies but the cost of actually killing someone is very high (prison and/or retaliation).
If a gangster is obliged to shoot at another gangster, he is much better off not just missing but also signalling to his opponent that he is not trying to actually trying to kill him. Holding a pistol sideways like an idiot is one way to signal intent to miss. Holding an AR-15 with an EOTech while wearing a ballistic vest signals the opposite.
The practice of shooting at someone with the intention of missing goes back to the days of duels. To delope is to throw away a shot. Alexander Hamilton infamously let it be known that he intended to delope during his duel with Vice President Aaron Burr, but Burr shot him dead anyway.
[ Many thanks to jdun1911 & mrsatyre for emailing me the tip. ]