When the Bruins played Arizona State last season, everyone saw Jack standing on the sideline as the Sun Devils' offense went up and down the field en route to a 35-13 halftime lead.
Jack only played on offense in the 38-33 loss that ultimately decided the Pac-12 South, and the decision not to use him on the other side of the ball was even second-guessed by UCLA coach Jim Mora.
This time around Jack is focused on defense, which he termed his ''main job,'' heading into the conference opener for the 11th-ranked Bruins (3-0) when they face the No. 15 Sun Devils (3-0) in Tempe, Arizona, on Thursday night.
''Myles is a big playmaker for us,'' linebacker Eric Kendricks said. ''It's going to be huge having him back.''
Even as some on the UCLA sideline were pushing for Jack to go in and try to slow down Arizona State, Jack himself said it was never a realistic option as he did not know the defensive game plan or calls after practicing all week on offense.
''I wished I was on defense, but I put it on my shoulders like, `What could I have done more on offense to help the team?''' said Jack, who rushed for 86 yards and a touchdown.
Now Jack is more comfortable preparing for both roles, totaling 13 tackles and 21 yards rushing with one touchdown in the two games he has been used on offense and defense this season. But against Arizona State, Jack is focused squarely on how to contain running back D.J. Foster.
Foster had been the focal point of the Arizona State offense this season long before quarterback Taylor Kelly hurt his foot against Colorado, ranking second in the FBS with 216.3 all-purpose yards per game.
He also ranks fifth nationally with 170 yards rushing per game, while his six total touchdowns are tied for the Pac-12 lead.
''Stats don't lie,'' Kendricks said. ''I feel like he is one of the best we've seen thus far, and maybe in the nation. He's running the ball hard. He has a lot of aspects to his game that are elite, and we're going to treat him as such.''
With fifth-year senior Mike Bercovici set to make his first career start, the Bruins expect Arizona State to lean even more heavily on Foster's dynamic skills carrying the ball and catching it out of the backfield or split out wide.
''He is pretty much their guy,'' Jack said. ''He does everything. He's a total back, and we're excited for a challenge like that.''
For Jack, it could frequently become a one-on-one challenge tracking Foster all over the field in the passing game. Jack has demonstrated the range and athleticism to do so, posting two interceptions and 11 pass breakups in his brief college career.
While Jack played exclusively on offense last season, Arizona State was able to capitalize by throwing to running back Marion Grice a game-high seven times for 72 yards.
Defensive coordinator Jeff Ulbrich said there are several other options in the Bruins' talented linebacker corps to cover Foster, but none might be as prepared for the assignment as Jack, who has plenty of experience as the focus of the opposing defense.
''I remember the Texas game, I looked up and all three of their linebackers were staring blatantly at me,'' Jack said. ''They knew what was about to happen.''
Even with the defense's eyes on him, Jack had five carries for 14 yards in the 20-17 win over the Longhorns.
Jack will get to return the favor against Arizona State, with his eyes on Foster at all times.