CULVER, Ind. (AP) Notre Dame opened practice Saturday looking to shore up a defense that was shaky at times last season.

The Irish lost six of the top eight tacklers on a defense that ranked 45th in the nation in total defense, allowing 372.7 yards a game.

The biggest challenge is replacing linebackers Jaylon Smith, who led the Irish with 114 tackles, and Joe Schmidt, the team's vocal leader. While three players will compete to replace Smith at weakside linebacker, the Irish know junior Nyles Morgan will take over for Schmidt in the middle.

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Coach Brian Kelly said Morgan, a former top recruit who struggled at first to learn the Irish defense, has gained the trust of defensive coordinator Brian VanGorder.

''The middle linebacker position is the most difficult position to get down and he's got it cold. He knows what he's doing,'' Kelly said.

Morgan started the last four games of his freshman season after Schmidt went down with an injury, but played sparingly as a sophomore, finishing with 17 tackles. Morgan said he knew he needed to stay patient and remain hungry.

''I couldn't give up. That wasn't a question,'' he said.

Up front, the Irish are hoping defensive tackle Jarron Jones can be a force again after missing all of last season with a torn MCL in his right knee. It was an injury he sustained when Schmidt fell into him during a practice last August. Jones, who practiced with the second team most of Saturday, admitted he played tentatively this past spring out of fear of another freak injury.

The 6-foot-5, 315-pound senior said he's determined to prove himself, saying he has to show he can outwork his teammates.

''Just show I can be a dependable player because this past spring I didn't show that,'' he said. ''I did a horrible job at that. I did a horrible job of being in shape. I let my injuries get the best of me.''

Kelly said the Irish hope Jones can contribute.

''I think 25 to 35 plays is a pretty good for a big guy like that, if he can give us explosive plays,'' he said.

The Irish also need some young players to step up in the defensive backfield and safety Max Redfield, another former top recruit, to play more consistently. Redfield was sent home before the Fiesta Bowl last season for being late to meetings.

''What we want to see is just that guy that does the basic things right,'' Kelly said. ''He was a guy that was up and down. We'd see great flashes and then we didn't see him for a couple of weeks. I think if we just get consistent play from him, we're going to get really good play.''

That's a challenge for an Irish defense overall that gave up too many big plays last season.

Morgan said he believes this year the Irish will be better on defense because they are ''nastier.''

''I can feel it. I can see it up front with the D-line, linebackers, safeties. It's just an attitude. It'd just attitude,'' he said. ''I love it.''