INDIANAPOLIS (AP) -- Indianapolis Colts linebacker Robert Mathis wasn't all that thrilled being called for an offside penalty on the final day of minicamp this week.
"I'm not exactly happy with that," Mathis said with a laugh.
The official that made the call? Sarah Thomas, who is on her way toward becoming the first permanent female official in the NFL. It could happen as early as the 2014 season.
"I'm certain I can't make everybody happy," Thomas said of that call on Mathis.
Thomas spent three days at the Colts minicamp as part of the NFL's officiating development program, and league officials say she would be the first woman to reach NFL fields through the program. She's expected to join the Colts in training camp next month and could call some preseason games this year.
Once completing the development program, Thomas could get a shot at the regular season if a spot becomes available. That wouldn't happen until a current official retires or leaves the league.
"It's just something that happened," said Dean Blandino, the NFL's vice president of officiating. "She was in our pipeline for a while."
Last year, Shannon Eastin became the first woman to be an official in both a preseason and regular-season NFL game. She was a line judge in the Rams-Lions season opener, among the replacements hired during the officials' lockout.
Eastin, who started officiating high school games before moving up to colleges, owns a company called SE Sports Officiating, which trains officials in football and basketball.
Last summer, the NFL Referees Association said Eastin shouldn't be allowed to work league games because she has been in the World Series of Poker. If Eastin is hired permanently, the NFL's gambling policy would bar her from participating in such events.
Thomas is an official with Conference USA and has been for the past eight seasons. She still has some steps to take before she can get to the NFL. There are interviews and background checks to be done, and she will be evaluated during any NFL camps and preseason games she handles - as well as during the upcoming college football season.
Just like a player, it's a big step for an official to go to the next level.
"It's similar from when a players jumps from college to the NFL," Blandino said. "Getting used to that type of speed is important."
Thomas noticed the speed right away at minicamp even when the players run with no pads. It will take some time to get used to. But she said she likes the challenge of officiating. That's what got her interested in the job of wearing the stripes during football games, even as a high school football official in Mississippi, where she's called state championship games.
"The speed, yes, is there," Thomas said. "These are just phenomenal athletes on both sides of the ball. The game has a tendency to slow down the most snaps you get and repetition. So, hopefully, the more snaps I get, things will start slowing down a little bit."
Thomas shows many of the qualities and traits the NFL looks for in an official. She's confident and shows a command of where to go and what to do at all times. Having a female involved and the NFL showing its diversity, well, that's just a bonus.
"It's always a positive when there's diversity," Blandino said.
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