TEMPE, Ariz. -- Every time Arizona Cardinals quarterback Clayton Tune stepped into the huddle throughout training camp, veteran left tackle D.J. Humphries saw the same, even-keeled rookie standing in front of him.

It didn’t matter what happened the play before, Tune wouldn’t get rattled.

“His poise is always on point,” Humphries said.

“That’s something I’ve liked about him. From the first time he came in the huddle in camp to any reps he has now, his face looks the same. He doesn’t look like the moment is too big for him, so that’s always big when you got a rookie in there.”

Tune, who was Arizona’s fifth-round draft pick (No. 139 overall) in April, is battling recently acquired Joshua Dobbs to be the Cardinals’ starting quarterback in Sunday's season opener against the Washington Commanders (1 p.m. ET, Fox). Coach Jonathan Gannon said he wanted the team to maintain a competitive advantage by not announcing a starter before the game, leaving everyone but the players behind closed doors in limbo. If Tune gets the start, he would be the lowest-drafted quarterback to start a season opener as a rookie since Randy Hedberg in 1977, according to ESPN Stats & Information.

After spending most of OTAs and minicamp running the second-team offense, Tune was the No. 2 QB during training camp and the preseason. He showcased an impressive arm and an understanding of a pro-style offense that’ll be run-heavy and feature two tight ends -- different from the Air Raid he ran at the University of Houston, which is a pass-first system that typically utilizes four or five receivers. He finished the preseason 34-of-59 (57.6%) for 353 yards with a touchdown and an interception.

“The way he's kind of committed himself to learning the offense, understanding the NFL game, doing things the way that we need that position to do them, it's been really fun to watch,” offensive coordinator Drew Petzing said. “His growth has been tremendous. Really excited about where he's at.”

He’s essentially been under a “waterfall of information” in the quarterback meetings, Gannon said. But what’s stood out to the first-year head coach was how Tune walked him through his mistakes -- what happened, why he made them, how he plans on fixing it.

“He's brutally honest,” Gannon said. “He says, ‘Yeah, I messed that one up,’ you know what I mean? And that happens. It's good. Let's learn from it and keep going.

“But I like that he plays fast. He has command when he walks into the huddle. You see the arm talent. So, he's got a long way to go, just like everybody does, but he's doing a good job.”

A few times during the preseason and training camp, Tune was too high with his passes. But he and Gannon said there was an easy fix: Step into the throws more and make sure his hand is over the ball.

There are parts of the NFL game Tune is still getting used to, such as having greater responsibility in the run game and with protections.

“You see a lot more coverages than we did [at Houston],” Tune said. “And just going through reads and being quick and concise with my footwork.”

One of the biggest adjustments the Cardinals have had to make for Tune coming out of Houston’s scheme was that footwork, Gannon said. But Tune's arm has impressed his coaches.

“If you can sling it,” Gannon said, “you can sling it.”

And Tune can.

As a senior at Houston in 2022, the 24-year-old Tune had 40 passing touchdowns (ranked third nationally), 313.4 passing yards per game (ranked fifth) and 25.69 completions per game (ranked seventh). He finished his Houston career second in school history with 104 touchdowns.

Between the playcalls, motions and watching the defense, running an NFL offense has been an adjustment. But Tune has seemingly embraced it.

“It’s fun to have a lot more on my plate,” he said.

Tune has also been comfortable in a huddle. Houston, he said, huddled about 60 percent of the time, which he said catches most people by surprise considering the Cougars ran the Air Raid.

“The huddle mechanics isn't foreign to me,” Tune said. “Just the mike and the headset, that's a little bit different, but the huddle itself is nothing new.”

He's gotten more comfortable with every practice, which grew his confidence. His goal was to find one thing to improve on every day. After practice or a game, he’d watch the film, take notes and work on them the next day.

His teammates noticed the incremental improvement. Wide receiver Marquise Brown didn’t see Tune make the same mistakes during training camp that he made in the spring.

That largely comes from the reps he’s been getting, which is more than most third-day rookies see during their first training camp.

Tune also got work during training camp with some of the first-team offense, preparing him to play with the starters if necessary.

“There's that belief that more reps are better for a young guy,” Petzing said. “I think there's certainly some truth to that, but there's also a lot of value in sitting back and watching guys do it, who have done it at a high level, who really understand the game.

“And he's done a great job, I think, of balancing the two.”

Petzing said this week that he’s “very comfortable” should Tune play Sunday in any capacity.

Going through a baptism by fire of sorts has prepared Tune to possibly make his NFL debut. During the preseason, Tune saw more defensive schemes than Gannon expected him to. That was a benefit for the Cardinals, Gannon said, because he’d rather Tune face them for the first time in the preseason than in, say, Week 5.

“The more and more that I know what I'm doing, the more I trust what I'm seeing,” Tune said.