R.I.P. to the UCLA run defense

The autopsy may be pending, but a forensics examination of UCLA’s badly mangled run defense is already well under way.

Injuries have been a factor, certainly. So has the youth movement required by continually replacing wounded players among the front seven. Tackling has been a problem among new and old players alike.

Bruins coach Jim Mora also pointed out earlier this week that linebacker Kenny Young and defensive end Jacob Tuioti-Mariner were the only players up front with any significant experience heading into the season after the team lost Takkarist McKinley, Eddie Vanderdoes, Eli Ankou and Jayon Brown to the NFL.

UCLA has continually restocked its roster with top-25 recruiting classes, but even the most highly rated players can take time to perform adequately at the college level.

“They’re talented,” Mora said of his young players, “but they’re inexperienced, and when you’re playing with inexperienced guys, you tend to have inconsistencies.”

Those irregularities have added up to some unsightly numbers. UCLA has allowed 2,729 rushing yards this season, putting it 65 yards short of a school opponent record with at least three games left starting Saturday when the Bruins (4-5 overall, 2-4 Pac-12 Conference) face Arizona State (5-4, 4-2) at the Rose Bowl.

The Bruins gave up a school-worst 2,793 rushing yards in 2005 on the way to a 10-2 season that included a victory over Northwestern in the Sun Bowl. UCLA currently has a less pleasurable connection to the Wildcats: The Bruins are giving up a worst-in-the-nation 303.2 rushing yards per game, putting them on pace to become the first team from a Power Five conference to give up at least 300 yards per game on the ground since Northwestern did so in 2002.

Mora said the run defense’s struggles are not a result of personnel failing to fit the style of defense he wants to play.

“You’re always going to step back and say, ‘OK, are we doing the right thing in recruiting and matching players to scheme?’” Mora said. “And I believe we are.”

The list of players who have missed games because of injuries or ailments includes defensive linemen Jaelan Phillips, Boss Tagaloa, Matt Dickerson and Rick Wade as well as linebackers Young, Josh Woods, Krys Barnes, Breland Brandt and Lokeni Toailoa.

The resulting patchwork defense has given up individual runs of 80, 72, 71, 69, 66, 62, 58, 43, 39, 37, 37, 34, 33 and 25 yards this season. Breakdowns in tackling among the secondary have contributed to some of those plays.

“We haven’t tackled well enough on the back end to prevent so many of those long gains,” Mora said. “It’s those explosive runs that have made our yards per game and yards per attempt just look so incredibly bad. We’ve given up so many — and I’m not talking about 15-yard runs, I’m talking about really long runs.”

The Bruins are giving up 6.0 yards per carry, putting them on pace to break another school opponent record (the 2005 team allowed a school-worst 5.4 yards per carry).

UCLA’s defense might get tempted to run the other way against Arizona State. The Sun Devils are coming off a 41-30 victory over Colorado in which they tallied 381 rushing yards, their highest total in a conference game since 1997. Tailback Demario Richard (189 yards) and quarterback Manny Wilkins (95) both set career highs in rushing yardage and tailbacks Eno Benjamin and Kalen Ballage added a combined 93 yards on the ground.

Arizona State also features several dynamic receivers, preventing the Bruins from a singular focus with their defensive plan.

“You can’t take everybody,” Mora said, “and commit them to the run.”

Hurry back

UCLA cornerback Darnay Holmes must sit out the first half of the game against the Sun Devils as punishment for his targeting ejection during the Bruins’ 48-17 loss to Utah last week.

Phillips is considered questionable because of an unspecified injury that kept him out of practice early in the week.

“We’re planning that he won’t be with us,” Bruins defensive coordinator Tom Bradley said, “and hoping that he will.”

ben.bolch@latimes.com

Twitter: @latbbolch