The first three games of the season were not kind to the Massachusetts football team’s run defense.

So far, the Minutemen are allowing 323 yards per game on the ground, which is second worst in the Football Bowl Subdivision (out of 123 teams).

These troublesome defense stats weren’t just the result of a single team putting on a show against UMass; this has been a recurring theme throughout games against opponents Wisconsin, Kansas State and Maine.

The Minutemen allowed three Wisconsin Badgers to run for over 100 yards each and a total of 393 yards in their season-opening loss. UMass did better in its second game against Football Championship Subdivision member Maine, allowing the Black Bears to run for 247 yards. The Kansas State Wildcats ran for over 300 yards against the Minutemen defense on Saturday.

One of the main issues for the run defense against Kansas State was that neither defensive lineman Galen Clemons nor linebacker Steve Casali could play in the game, due to injuries. This led to a lack of depth on the line and at the linebacker core.

“Those two guys,” UMass coach Charley Molnar said, “they change the complexion of how we rotated our players in … We just don’t quite have enough guys that are ready to play and help you play winning football against a team like Kansas State.”

Even though rush defense is often attributed to defensive line play, Molnar is pleased overall with the play of his linemen, and he doesn’t believe that they are struggling against the rush.

“It’s not been the defensive line,” Molnar said. “That’s not been the issue. The defensive line has done a really good job of holding their gap. We’ve been out of our gaps, there’s been some plays that have been attributed to the D-line.”

The total of rushing yards isn’t the only troubling run defense stat. The Minutemen are also allowing an average of 7.2 yards per carry and have allowed their opponents to score on rushing touchdowns nine times. Many of these scores have come on big plays as well, including a rushing touchdown of at least 26 yards in each of the first three games this season. Molnar said that this issue is coming from defensive positions other than the line.

Perhaps the most puzzling stat of all on the defense, however, is that UMass has a passing defense that stacks up with some of the best in the country. The Minutemen are allowing just under 200 yards through the air per game, which shines light on the issue of the run defense versus defending the pass.

Two young players who have the potential to help out the rush defense are linebackers Kassan Messiah and Jovan Santos-Knox, but neither player showed up in the statistics on Saturday. Both players saw their fair share of playing time during their freshmen seasons, and a lot was expected from them going into 2013.

Molnar stressed that he can’t have those two players take a step back this season.

“Those two young guys have stepped up,” he said. “They improved. They played a ton last year, got better in the spring, during summer camp and now we can’t have them flat line. We need them to continue to grow.”

While the young players on defense continue to grow, expect teams to try to take advantage of UMass’ glaring weakness against the run. Next up: Vanderbilt on Sept. 21 at Gillette.

Cameron McDonough can be reached at [email protected] and followed on Twitter @Cam_McDonough.