This term is an adjective that refers to specific players on a basketball court.
For someone to be Josh Smithin, they must be trying to do a nasty dunk when ever touching the ball. They also tend to hold on to the ball for long periods of time, waiting for their moment to hit the lane, jump over some niggas, and fucking slam the ball in the hoop.
Some kid, who you thought couldn't do shit, just jumped from the free throw line and jammed the ball down another niggas throat.
Person: Damm that fucka be Josh Smithin!