"I don't think we were mentally prepared for this game," said Guards Coach Ronaldo Aguirre. "A lot of horsing around, not taking it seriously.
"But we'll learn from it. We know we have to regroup and try much harder than this."
Although officials called for a break in the game with 3:36 left in the first quarter because of lightning, it did little to disrupt momentum.
Malibu (2-2) scored on its first five drives in the first half en route to a 28-6 lead.
Bell-Jeff scored with 4:53 left in the half on an eight-play, 64-yard drive, capped by a one-yard run from sophomore running back Demitri Moreno.
It was the first of two touchdowns for Moreno, who finished the night tallying 27 yards on nine carries.
Moreno helped fill in for junior running back Joshua Martinez, who was hurt at the start of that scoring drive.
Martinez, who had scored eight of the team's 10 touchdowns entering Friday's game, apparently hurt his right knee on a 20-yard return that gave Bell-Jeff the ball at its own 36.
Martinez returned into the game on that same drive, but he hurt himself on the last play of the half and did not return. He finished with four yards on three carries.
"He got speared on the leg," Aguirre said. "I know these teams and I told Josh, 'You're going to get cut.' And I knew for sure he was going to get cut. It happens. It's part of football. You have to be careful.
"They knew they had to take him out. He's my best player."
It was a devastating loss for the Guards, who saw Martinez average 10.11 yards per carry entering the game.
Malibu led, 42-6, at the end of the third quarter, allowing for a running clock the rest of the way.
Bell-Jeff scored again with 5:36 left on an eight-yard touchdown from Moreno.
Sophomore Eric Agaverdyan led the Guards in rushing with 68 yards on eight carries. And quarterback Mitchell Kellog, who did not attempt a throw until the last play of the third quarter, completed two of four passes for 43 yards.