Senior linebacker Porter Gustin leads the Trojan defense with 4.5 sacks so far this season. (Sarah Kim | Daily Trojan)Throughout the opening four games of this season, the weakest link for the Trojan football program has been the defensive secondary. With sights set on Arizona — and the team’s explosive quarterback, Khalil Tate — head coach Clay Helton emphasized mental toughness as the Trojans hit the field for practice on Wednesday.Helton acknowledged that Tate has a versatility of strengths, including the ability to drop balls deep, forcing defenses to spread thinly across the field to adapt to the quarterback’s wily triple threat on the ground, in both the short passing game and deep in the field. “[We need to keep] contain on probably the most dangerous quarterback that we’ll face all season,” Helton said. “You see some of the dimes he’s dropping in on deep balls once the play is broken down … [and it] is unique. We’ve got to be able to keep him in the pocket and keep him contained.”The Wildcats are averaging over 270 passing yards per game, and Tate posted close to 350 passing yards against Houston and Southern Utah. Although he has been held to less than 20 yards rushing per game, Tate is known to rip off big gains on his feet when given a big enough hole to blast through.“You put [redshirt sophomore running back] J.J. Taylor with 260 yards of passing, and that’s a dangerous offense,” Helton said.Tate has yet to notch a victory over the Trojans, however, suffering a loss on his home field and in the Coliseum. As he prepares to host USC for his team’s first home field game against a Pac-12 opponent on Saturday, the junior quarterback will be anxious to even that record.“A dual-threat quarterback is always tough,” senior linebacker Porter Gustin said. “But we know what he can do and we know what he’s capable of. We’ve got to prepare for that. It’s like they’re playing with an extra man out there.”This will be a major test for the Trojans, whose main struggle so far this season has been to create a solid passing defense. The team allowed Washington State quarterback Gardner Minshew II to throw for 344 yards and three touchdowns last week, failing to pick up an interception and allowing the quarterback to throw 71 percent.“When you play man coverage, you don’t see a ton of picks. You see a lot more in zone coverage,” Helton said. “We do have a lot of past break ups, hopefully we’ll get our hands on the ball a little more. It also comes with tipped balls. … Hopefully we’ll get some more of those too.”The secondary in particular struggled with deep passes, allowing Cougars receiver Easop Winston Jr. to average almost 24 yards per carry and grab a 59-yard touchdown lob. Against Tate, the unit will be forced to tighten up or pay up.The Trojans also struggled to challenge the passer and collapse the pocket, with Gustin recording the lone sack in the game against Washington State. Without heavy pressure in the face of the quarterback, Tate will be free to pick off receivers left and right, leaving the secondary wide open.One key change could be the introduction of true freshman corner Olaijah Griffin to the starting lineup. Griffin has slowly made his way into a regular rotation for the Trojans, standing out in last week’s game against Washington State. During Wednesday’s practice, the freshman earned first-team reps. He finished practice with a pick-six, earning howls of approval from his teammates on both sides of the ball. Griffin could provide a much-needed spark to the Trojan secondary.Injury reportRedshirt freshman defensive lineman Jay Tufele, who blocked the game-winning field goal attempt in Saturday’s game against Washington State, returned to action. Gustin and sophomore offensive tackle Andrew Vorhees both participated in practice, but on a limited basis. Gustin is still nursing a knee injury, and Vorhees is recovering from a sternum contusion. Both are expected to make full returns by game time on Saturday.Freshman receiver Amon-Ra St. Brown remains limited with an AC shoulder sprain. Redshirt freshman outside tackle Jalen McKenzie also sat out practice with a strained back.