Armstrong admitted this week that when his opportunity came, by way of an injury to Martinez, he wasn't as prepared as he should have been.
Martinez is gone now, and so is co-backup Ron Kellogg III. Armstrong will head into preseason practice as the presumed starter, and the rising sophomore is using this spring to assert his ownership of the job.
"I've worked as hard as I can because I know next fall, it's just going to be me," Armstrong said. "I've got to make the coaches happy, make sure my team has my back and make sure when things are going bad I'm the person who gets the team up. Last year I kind of struggled in those areas."
Nebraska won seven of the eight games Armstrong started in spite of his problem with turnovers. He threw eight interceptions, and his rate of one for every 16.3 passes was the fourth-worst mark in the Bowl Subdivision for quarterbacks with at least 100 attempts, according to STATS. He also had two game-changing fumbles in a loss to Michigan State.
Armstrong's priority this spring has been to be smarter about when and where to throw the ball. On more than 300 passes this spring, he said, he's been intercepted only three times.
"He doesn't compound errors like last year," offensive coordinator Tim Beck said. "I don't know that anyone has ever played a mistake-free ball game. The worst thing a guy can do is make two in a row. He makes one mistake because he reads the wrong guy and then he throws it and it's intercepted.
"If he reads the wrong guy, run it. Get a yard or 2 and we'll be OK. It's tough to live with two mistakes, and that's what we're trying to cut down at this point."
Armstrong showed promise last season. He combined to go 20 of 28 with three touchdowns and no interceptions in back-to-back home wins over South Dakota State and Illinois. He completed 5 of 7 passes during the winning, 75-yard touchdown drive at Michigan. He threw a 99-yard TD pass in the second half to break open the Gator Bowl win against Georgia.
But he was picked off three times while splitting time with Kellogg in a win at Purdue. After he threw three interceptions at home against Northwestern, including one that set up the Wildcats' go-ahead touchdown late in the fourth quarter, Kellogg came in and heaved the Hail Mary that won the game.
"When my number was called, sometimes I responded and sometimes I didn't," Armstrong said. "Ron saved me sometimes."
Armstrong turned his ankle in the first quarter at Penn State, and Kellogg came in to lead the Huskers to an overtime win. The injury kept Armstrong out of the final regular-season game, a loss to Iowa, and had him feeling sorry for himself.
He said his outlook changed after coach Bo Pelini called him one night before the team began practicing for the bowl. Pelini's message: the offense is now yours, and you need to act like it.
"I matured a lot. And I matured fast," Armstrong said. "I understand that I'm going to make mistakes. It's how you respond. Last year, I wasn't good at responding to mistakes. It was like a domino effect."
Receiver Kenny Bell said Armstrong is a natural leader and has never outwardly shown a lack of confidence. If there's anything different about Armstrong this spring, Bell said, it's that he demonstrates a greater sense of purpose.
"His swagger hasn't changed," Bell said. "What's changed is his commitment and how he works every day."
Always a vocal leader, Armstrong is even more so this spring, teammates said. He also has improved in the zone-read game, and he's been sharp throwing the deep ball.
"I feel like I'm physically fit for another season, and I've worked hard in the weight room and it's showing out here," he said. "Now I've got to stay focused and make sure I put my teammates in the right positions."