Most years, there are about 3.5 to 4.0 return touchdowns per team season in the NFL, or about 115 in the entire NFL. But in 2016, there were just 73 return touchdowns, the fewest in a single season since 1988. I’m defining a return touchdown as a punt return, kickoff return, fumble return, or interception return for a score; this does exclude some unusual returns, such as a blocked field goal return, blocked punt return, missed field goal return, etc.

By this measure, the average team had just 2.3 return touchdowns last year. That’s a pretty unusually low number:

So what’s driving the decrease in return touchdowns? Well, return touchdowns are down across the board. From 1996 to 2015, there were 0.47 punt returns per 16 team games; that number dropped to 0.31 last year. There were 0.42 kickoff return touchdowns per 16 team games from ’96 to ’15, and just 0.22 last year. And when it comes to fumble return touchdowns, there were 0.93 per team season over the prior 20 years, compared to just 0.69 last season. So all three categories saw a dip of about 0.2 per 16 games in 2016, at least relative to the previous two decades.

But there’s no doubt that the biggest decline is in pick sixes. In fact, the decline in interception return touchdowns equals the decline in the other three categories combined: there were 1.67 pick sixes per 16 games from ’96 to ’15, and just 1.06 last season.

In 2012 and 2013, there were an average of 68 pick sixes in the NFL. Last year, there was just half as many. One-year blip, or sign of a new trend?