The second-year player is part of a defensive unit that carried the Colts early in the season. But on Sunday, the defense started strong before struggling the rest of the way when the offense was scrambling to get back in the game in a 42-34 loss to the New York Jets.
"Definitely, we're frustrated," Walker said. "We're young -- don't want to hear that. We're a young team, but we're in the NFL. We had our chances but didn't make them. We have to make sure this isn't something that carries over."
Statistically, the Colts haven't been one of the best defenses in the NFL this season. What they've been, though, is an opportunistic unit. They have 17 sacks and have forced nine turnovers through six games, including two in the first half Sunday.
The bend-but-don't-break defense didn't do its part against the Jets. The Colts made Jets rookie quarterback Sam Darnold -- the No. 3 overall pick in April -- look like a six-year NFL veteran. He started the game 11-of-12 and finished 24-of-30 for 280 yards and two touchdowns.
"It wasn't really what they were doing," said Colts rookie linebacker Darius Leonard, the NFL's leading tackler. "It was about our mistakes. We had a lot of mistakes on defense. It's what we weren't doing."
The most telling stat of the Colts' performance was that they forced the Jets to punt only once. It's hard to beat any team in the NFL when you can't force punts, even if 21 of the Jets' points came via seven field goals.
It didn't seem like the defense was going to have issues when it forced back-to-back turnovers -- an interception and fumble -- on the Jets' second and third possessions, respectively.
Then the issues started for the Colts. Take away the knee to end the game, and the Jets scored on eight of their final nine possessions. The Jets started in Indianapolis' territory on four of those scoring drives because of turnovers or turnovers on downs by the Colts.
Darnold didn't do anything extraordinary to beat the Colts. He simply found the soft spots in the Colts' Cover 2 defense over and over again. He made quick-out throws to the sideline and took what the defense gave him.
"It seemed like when we played zone, he did a good job of staying patient and hitting guys underneath," Colts coach Frank Reich said. "Then a couple of times when we played man, their receivers won some of their one-on-one battles, and that's the thing. When you win your one-on-one battles in man coverage, it sometimes results in a bigger play, and they hit a few chunk plays as a result of that."
Missed assignments. Poor fundamentals. Lack of communication. Those are all areas in which the Colts have struggled in the past and areas in which they believed they had improved this season.
"It's about us paying attention to detail," Colts linebacker Najee Goode said. "We've done a good job in that area this season. When you don't pay attention to the littlest of details, you are more prone to make mistakes. That's what happened to us."
The Colts could be facing Bills backup quarterback Nathan Peterman when they host Buffalo in Week 7. It doesn't matter whom they face, though, if they can't get stops. They're giving up an average of 322 yards passing the past three games, after giving up an average of 241 the first three games.
"It's stuff we know we can get correct and need to get fixed right now," Walker said. "We got beat by beating ourselves. We can't have that. Everybody is too good in this league. The players are too good. When you have critical errors and mistakes, you're never going to be able to help yourself."