The 75 greatest players in NBA history, ranked by Player Efficiency Rating (PER)

60.    Allen Iverson-20.92

It shouldn't come as a surprise that Hall of Famer Allen Iverson ranks so low in PER, given how it values efficiency. Iverson was known as a prolific scorer during his heyday but he wasn't nearly as efficient as players today. That is probably due to shot selection, with Iverson favoring mid-range jumpers over threes and floaters in the paint. 

He, despite his explosive athleticism, was only listed at 6'0 tall but likely even shorter. Scoring against tall players on the perimeter and among the trees in the paint is much harder to do but Iverson did, albeit not as efficiently as he potentially could have.

Once he was traded to the Denver Nuggets, his offensive efficiency improved dramatically with better shot selection and less of a green light playing next to Carmelo Anthony. That at least proves that he could have ranked significantly higher in PER, which actually penalizes players for negative things like missed field goals and turnovers. 

Iverson not shooting a high volume of threes resulted in him often taking more than 20 2-point shots per game, which are valued at 1.65 points and him missing well over half. He also led the league in turnovers, though he also led the NBA in steals four times. Iverson gives, and Iverson takes away.

Ultimately, he was still a great player and might've thrived in today's NBA but was held back by a number of factors.