For the first four games of the 2014 NFL season, the Indianapolis Colts’ Sergio Brown was a backup behind safety LaRon Landry, a hard-hitting, high-priced free agent and former Pro Bowler. Brown, a Notre Dame alum, was undrafted out of college and unceremoniously cut by his previous team, the New England Patriots, before the start of the 2012 regular season. When the Colts picked him up, Brown was happy just to have a job and make a contribution playing special teams.

Then came September 29, when Landry was suspended four games for a failed drug test. Brown felt bad for his teammate. But he also recognized the opportunity in front of him.

He would get the start versus the Baltimore Ravens on October 5.

Brown practiced with the first-team defense all week, but reality didn’t sink in until game time. “I didn’t really even worry about it too much,” he says. “I was just like, ‘I’ll wait ’til the time comes,’ and then once I’m out there starting, it was like, ‘Oh, my God. Finally.’”

Brown had a great game, recording three tackles, deflecting a pass, and sacking Baltimore quarterback Joe Flacco on a fourth-down play.

“The reason I went to Notre Dame was because of my father and the things that he did. But that’s the person he was in my life.”

The day was also meaningful because it marked the 12th anniversary of his father’s death. “It was just very easing,” says Brown. “It gave me peace of mind, peace of everything, because he was my biggest supporter in athletics my whole life. It was motivation. It was just, like, no worries for me. It was a big burden off. All the stress and anxiety that I did have going into that game—when it finally happened, I put the two dots together. It was like a big exhale moment: ‘Let’s go do this.’”

Brown has played consistently since that first start, averaging just over two tackles and 1.5 pass deflections per game. On November 3, before the team’s bye week, he got to showcase his talent on a national stage, logging two deflected passes in the Colts’ 40–24 Monday-night win versus the New York Giants.

Landry was reactivated after the Giants game. But Brown’s performance in Landry’s absence probably helps explain why the Colts’ coaching staff has been in no apparent hurry to insert Landry back into the starting lineup: Head coach Chuck Pagano indicated this week that when the defense takes the field Sunday against the Patriots, Brown will get the nod—and a chance to show his former team why they shouldn’t have cut him.

Brown credits his father, Mario Brown, with laying the foundation for his surprising success with the Colts. It was Mario who first encouraged Sergio to pick up football. And he became a forceful advocate for his son early on, which sometimes got him into trouble. When Mario got kicked out of Sergio’s Pop Warner football games, the father would resort to knocking on neighbors’ doors and asking them if he could watch the game from their backyard, where he would resume yelling out his support and encouragement. Mario was also a fixture in the local community and would push Sergio and other young people to get good grades and do their best, playing the role of father figure to others besides his son.

Mario later talked his way into the office of then–Notre Dame head coach Tyrone Willingham’s office while Sergio’s brother, Nick, was playing in a summer basketball tournament there. He told Willingham that Sergio, though still years away from attending college, was going to play football at Notre Dame.

Sergio wasn’t even thinking much about football at the time, as basketball was his favorite sport; he played both at Proviso East High School in Maywood, Illinois, 12 miles west of Chicago. Sergio thought Mario Brown’s encounter with Willingham was just his dad being himself, seeking out the person on campus best able to help his son and then selling him.

“That story stuck into me, and when Notre Dame offered me (a scholarship), it was a no-brainer to go there,” says Sergio. “That’s the reason why I went to Notre Dame. It was because of my father and the things that he did. But that’s the person he was in my life.”

Brown played at Notre Dame from 2006 to 2009, handling special-teams duties during his first two years and then becoming a fixture at free safety his final two seasons. The Patriots signed him as an undrafted free agent in 2010 but cut him after two seasons. Within two hours, Pagano called and told Brown he was coming to the Colts, catching him and his agent off-guard.

“I just really want to play football. The love and the joy I get out of it eats me up on the inside.”

When Brown arrived, he was struck by the contrast in cultures. New England was more structured and rigid, and in Indianapolis there was a balance of being looser while still treating the game like a job. The difference was especially noticeable when he encountered general manager Ryan Grigson, who called Brown a “werewolf” during their meeting, a label he repeated when the two sat down with Coach Pagano.

“I still don’t know what a werewolf is,” says Brown, laughing. “He walks me to Coach P’s office, calling me a werewolf again, and then Coach P got all of this energy, and I’m like, ‘This is night and day from New England.’”

One of the things Brown likes about Indianapolis is how friendly everyone in the organization is, from top to bottom. He says all of the defensive backs are friends, and everyone hangs out with each other. For him, being a member of the Colts doesn’t even feel like a job.

“It’s more of a family environment than a work environment from the top down,” Brown says. “I could sit and have a 15-minute conversation with DeWitt Jackson, the organization’s head chef. That’s how much of a family the organization is, and how much we are together. I would probably call him one of my favorite people in the whole organization. Everyone’s positive, got good energy. It’s a great work environment.”

On the field, Brown says he is motivated by a “chip on the shoulder” mentality, which goes back to his days at Notre Dame and New England, where he felt he had to prove himself to everybody.

“I just really want to play football,” he says. “The love and the joy I get out of it eats me up on the inside.”

