KNOXVILLE, Tenn. (AP) — Tennessee's constant struggles on offense are hindering its defense.

Each of the last two weeks, the defense has started out playing well and keeping Tennessee competitive even as the Volunteers (3-4, 0-4 SEC) have struggled to move the ball. Then the defense spends so much time on the field that it wears down as its lack of depth gets exposed.

Against top-ranked Alabama last week, Tennessee only trailed 7-0 with five minutes left until halftime but eventually fell 45-7 . One week earlier, Tennessee led South Carolina 9-3 at halftime before losing 15-9 as the Gamecocks possessed the ball for nearly 21 minutes in the second half .

"We talk about playing complementary football," Tennessee coach Butch Jones said. "Obviously we've not performed like we'd like to on the offensive side of the ball. We've had way too many three-and-outs. I believe we only had 46-odd (offensive) plays against Alabama. That really puts your defense in a difficult situation. We have to fight through that. We have to keep grinding."

Tennessee's offense hasn't scored a touchdown in its last 14 quarters and plays Saturday at Kentucky (5-2, 2-2 SEC) without its leading rusher and top overall player. Running back John Kelly was suspended along with backup linebacker Will Ignont for Saturday's game after they were cited this week on misdemeanor marijuana-related charges.

"I understand that my actions were immature and selfish, and I realize they have an impact on more than just myself," Kelly said Thursday morning via Twitter . "I take full responsibility and accept the punishment that I have been given."

Kelly's absence puts even more pressure on a defense that is performing slightly better than last year, though it's not evident from the Vols' winless record in SEC competition.

Tennessee is yielding 26.9 points per game, 405.1 yards per game and 5.78 yards per play. Last season, the Vols allowed 28.8 points per game, 449.2 yards per game and 5.84 yards per play.

"In the big picture, we have to put a whole game together," defensive coordinator Bob Shoop said, "and that's what we haven't been able to do yet."

The Vols have made that modest improvement despite losing first-round draft pick Derek Barnett and third-round selection Cam Sutton to the NFL and dealing with major injuries to key players.

Tennessee lost arguably its top returning defensive performer when linebacker Darrin Kirkland Jr. suffered a knee injury that prevented him from playing at all this season. The Vols' top tackler last season was safety Todd Kelly Jr., who also is out for the year with a knee injury after playing just two games.

Linebackers Cortez McDowell and Austin Smith have played a combined total of five games because of injuries. Backup safety Evan Berry has played in only one game all year due to injury. Tennessee's depth on the defensive line took a hit with the suspension of Darrell Taylor , who is expected to miss a third straight game this week.

"No excuse," linebacker Daniel Bituli said. "Coach Shoop teaches about it every week, that we have to step it up for four quarters."

The depth issues on defense have enabled some underclassmen to step forward.

Tennessee's top three tacklers are all sophomores: Bituli, safety Nigel Warrior and linebacker Quart'e Sapp. Bituli's 97-yard interception return against Alabama last week is Tennessee's only touchdown during its current three-game skid. Freshman cornerback Shawn Shamburger made his first career start against Alabama and had 12 tackles plus a sack.

Their presence gives this defense some hope for the future. In the meantime, no matter how much adversity it faces, Tennessee's defense realizes it can't continue these second-half fades.

"It's a wear-down factor," Shamburger acknowledged, "but still at the end of the day, it's our job to keep the points off the board."

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