The world of the National Football League is definitively masculine. The pace of the game is fueled by the highest levels of testosterone. Arguably the most vigorous of all professional sports, there's no place on an NFL field for a woman, right?

There is now.

On Saturday, August 15, a barrier-breaking handshake took place on the University of Phoenix Stadium field before the Kansas City Chiefs took on the Arizona Cardinals in the first preseason game of the year. One hand belonged to Sarah Thomas, the other to Jennifer Welter.

The significance of this on-field greeting was framed as simply just another headline amid the other stories surrounding the return of real NFL football. However, the impact of what happened in Arizona that night may be felt throughout the league soon.

Thomas was named a full-time NFL official four months ago, becoming the first female to ever hold that position. She had worked preseason games and training camps in the past, and her appointment came after she was one of 21 finalists in contention for the job back in 2013.

While we had seen females in stripes before last Saturday (Shannon Eastin made her replacement officiating debut in 2012 during the referee lockout), we had never seen a woman work an NFL sideline while holding a coaching position. Welter was hired by the Arizona Cardinals on July 27 as an assistant coaching intern for training camp and the preseason.

The assistant linebacker coaching job is not permanent, however. When Coach Bruce Arians was asked by ESPN about the criteria Welter had to meet in order to get hired on full-time, his answer was unclear. "When are we going to have female coaches?" he responded. "The minute they can prove they can make a player better, they'll be hired."

With a master's degree in sports psychology and a Ph.D. in psychology, Welter has made the transition into an NFL locker room fairly seamlessly, all things considered. Cardinals players knew that Arians wouldn't bring someone in simply as a publicity stunt, so they trusted that she was serious about coaching.

One common concern that may have limited women's opportunities as coaches in the NFL was that they would change the dynamic of the team or that they would make players uncomfortable in the locker room. Linebacker Kevin Minter feels otherwise.

"She's kind of one of the guys, but she's not overbearing. She's just enough. She's right along with us. Our linebacker corps, we're carefree a bit," Minter told USA Today. "We joke around, we play, and I was hoping that she wouldn't change that. But she jumped right in with us."

This internship is a test, and Welter seems to be passing just fine so far. It's not just a test for her; it's a test for all female coaching hopefuls. How she finishes out the preseason and the impression she makes on players and coaches across the league will determine her next step.

A quiet chat on the field between an assistant coach and a line judge before a preseason game would ordinarily have no newsworthiness. But what we are seeing was a sign that, slowly but surely, a window for women to make their mark on the NFL is opening. Thomas' and Welter's continued successes this off-season will go a long way toward prying that window open even further.