There have been many theories about the rise in concussions in football and the reason for players’ long-term health issues.

In a Sunday report, National Public Radio said the players might be their own worst enemies. They have grown tremendously over the past few decades, and as players increase in size, so does the ferocity of their hits.

Timothy Gay, a physicist at the University of Nebraska and author of “Football Physics: The Science of the Game,” said science is catching up to the players.

Back in the 1920s, when the NFL was just getting started, the average lineman weighed only about 190 pounds. Now they average 300 pounds.

That means Hall of Famer Morris “Red” Badgro, who played for the New York Giants in 1930, would lay down quarterbacks with about 970 pounds of force, according to Newton’s second law (and a bunch of simplifications).

In contrast, Baltimore Ravens starting lineman Haloti Ngata weighs 335 pounds and runs the 40-yard dash in just under five seconds. If he sacks Colin Kaepernick on Sunday, he’ll unleash about 1,700 pounds of force.

In other words, getting stopped by Ngata is literally like having nearly a ton of bricks fall on you.

“These are very strong forces,” Gay says. “This is why they call football a contact sport.”

Athletes can usually handle these hits when the energy and force spread across the whole body, especially with the help from modern-day padding. But when the tackles are focused on small areas, like during a helmet-to-helmet collision, then the impacts become severe.

As for the effects of increasing mass on player concussions, that subject still is under discussion.

Vassilis Koliatsos, a neurologist at Johns Hopkins University, says doctors and scientists still are trying to figure that out.

“Faster, heavier, more aggressive players will absolutely increase the impacts,” Koliatsos tells Shots. “They are quite severe.”

But right now, he says, they don’t have scientific evidence about what links concussions to long-term brain injuries. “There’s even some concern that weaker, nonconcussive hits — although poorly defined — may also have something to do with it.”

- Bill Bradley, contributing editor