EAST LANSING -- The reasons for Michigan State's 2016 tumble from a Big Ten title to 3-9 have been thoroughly documented by now: injuries, underperformance, chemistry issues and a failure to finish close games all led to college football's biggest declines of last season.

But among the X's and O's reason for the 2016 struggles, the RPO is as good a place as any to start.

The offensive play, short for run-pass option, has given Michigan State's defense fits as it has gained popularity in college football in recent years.

On the list of issues for the coaching staff to address this offseason, defending the RPO was near the top, Spartans coach Mark Dantonio said.

"I think you have to reinvent your philosophy," Dantonio said of defending RPOs. "So a major part of our film study and off the field study has been investigating RPOs. What makes it, how to perform against it, how to perform with them."

In its most basic sense, an RPO is a play that involves a quarterback making a decision after the snap about whether to run the ball (either hand it off or keep it himself) or pass it.

That decision is made based on a read the quarterback makes on a defender, which tells him if a run play or a pass play could be more successful.

The play has been around in some form for years. Spartans defensive tackles coach Ron Burton said the first time he saw them used extensively was during the 2015 Cotton Bowl against Baylor.

But now, coaches say, they see them every week -- most often on the first play of a possession or a first-and-10.

"They're really in vogue now," Spartans defensive ends coach Mark Snyder said.

As RPOs have increased in usage, Dantonio has become more and more vocal about the need to make changes in stopping them.

"That's been a big part of what we're trying to do," Dantonio said.

The most obvious change made this offseason regarding RPOs was in coaching staff assignments. The Spartans moved Snyder from coaching linebackers to coaching defensive ends, while Burton moved from coaching the entire defensive line to coaching solely defensive tackles.

The move was partially to balance out player-coach ratios, but Dantonio said he also wanted to put more focus on defensive ends, a position group he says has been significantly altered by the rise of RPOs.

"I just felt like defensive ends with all the RPOs right now, you know, they're becoming a little bit more of a hybrid player," Dantonio said. "Are they big linebackers or, you know, what are they?"

As far as what other changes were made to improve RPO defense, coaches are reticent to give out too many details.

But a primary goal, coaches say, is to keep defensive end's feet moving when the come off the line of scrimmage. The confusion brought by RPOs can cause linemen to stop and effectively be taken out of a play. Michigan State notched just 11 sacks last year, third-worst in FBS.

Burton said a young group of defensive linemen having another year under their belt should help with that as well.

"Having an experienced group at defensive end and defensive tackle helps get you much better at understanding," Burton said. "If you have limited experience, you're less likely to understand the nuances of the RPO."

For linebackers, as outside linebacker Andrew Dowell, the challenge of defending an RPO is getting a read from an opposing quarterback at the same time that quarterback is trying to read him and make an RPO decision. He likened the situation to a game of chicken.

The changes made during the offseason, he said, will help him make that read better and faster than before, while making his own play more difficult for the opposing quarterback to read.

"We changed some things up in our base defense so I can react different and learn better," Dowell said.

Michigan State players and coaches hope an offseason full of study and tweaks will help them be better prepared for a play that gave them plenty of trouble last year. But they also know that RPOs aren't going away, and that defending them will continually be a challenge.

"We've changed a few things," linebacker Chris Frey said. "But no matter what defense you play, it's going to be hard to guard an RPO."