It's difficult to imagine a U.S. women's national team without Heather O'Reilly. She has represented the USWNT in the last three Olympics, winning three gold medals, and has been a steady presence on the team since she was 17 years old.

But now, at age 31 and still relatively close to her prime, O'Reilly won't play in an Olympics. When Jill Ellis named her roster headed to the 2016 Olympic Games in Brazil, O'Reilly was selected as an alternate, who can only be a late addition to the roster in the rare case of injury.

Though Ellis rattled off the names of players like Mallory Pugh and Crystal Dunn as players who emerged in the USWNT picture since last year and made it harder for O'Reilly, she eventually came around to Megan Rapinoe. In the end, Ellis' choice was between a Rapinoe who hasn't played since December after an ACL tear, and O'Reilly, who Ellis said pushed for a spot "to the very last day."

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"It is a very competitive position," Ellis said of O'Reilly's winger role shortly after the roster was announced on Tuesday. "I looked at a lot of things and form was a big part of that. With Rapinoe, it obviously was not her form because she hasn't been playing, but she's got set pieces, crossing, the pieces where I think late in a game or against a certain team we have to break down, she can help us with."

Comparing Rapinoe vs. O'Reilly conjures up memories of each delivering last-gasp, game-saving crosses. For Rapinoe, it was during the quarterfinal of the 2011 World Cup, when the cross she delivered to Abby Wambach's head turned into the latest goal in World Cup history and forced a penalty shootout against Brazil that the U.S. won. For O'Reilly, it was during the 2012 Olympics, when her cross to Alex Morgan's head became the latest goal in Olympic history and broke a deadlock for victory over Canada.

Both of them have delivered some of the most important crosses in the history of the USWNT, but Ellis clearly sees Rapinoe, who also regularly takes corner kicks, as having the superior skillset.

"Megan does have an 'it factor' in terms of what she can give us in set pieces and crossing," Ellis said. "She's one of the best crossers in the world. She has qualities in there that I felt that if she was healthy enough to play we would use."

It is the most controversial decision on the roster though. Rapinoe tore her ACL in December and it's a long, difficult injury to come back from. Although now is about the time a player would be expected to return from such an injury, bumps along the way aren't uncommon. After returning to full training last weekend, Rapinoe pulled her quad while practicing corner kicks. If Rapinoe does not play in the USWNT's final pre-Olympic friendly on July 22, that means she will make her return during the Olympics.

There is a precedent for such a move. Before the World Cup last summer, Alex Morgan was injured and hadn't played in a match in several weeks. She didn't return to full training with the team until it arrived in Canada for the tournament. Yet Ellis built her minutes through the tournament, starting her as a very late sub in the group stage and gradually as a starter in the knockout rounds. Ellis said she plans to do the same thing with Rapinoe.

That doesn't mean bringing Rapinoe isn't a risky decision -- the Olympic roster is only 18 players, compared to 23 during a World Cup, which means there's much less room for unproductive players. But it's a decision made easier by having O'Reilly as an alternate. If a player on the roster is injured, O'Reilly can move to the bench and, although it's a rare scenario, Ellis admitted it allowed her to select Rapinoe.

"Am I concerned?," Ellis said of putting Rapinoe on the roster. "I think many years ago when you'd name alternates and they wouldn't travel with you, you were really dealing with a small roster. Now, you travel with these alternates, which you can use anytime if there's a medical situation, so you have that in your back pocket."

With Rapinoe unlikely to be starting for the early rounds of the tournament, Ellis can rely on considerable depth on the flanks. While Pugh and Dunn are talented newer players who didn't play at last summer's World Cup, Tobin Heath remains a likely starter and Ellis has also been keen to push players like Christen Press, a natural central forward, out wide as well.

It's fair for Ellis to blame O'Reilly's exclusion on the depth at her particular position, but it only tells part of the story. It's not necessarily just that players like Rapinoe, Pugh and Dunn are better than O'Reilly; it's that they play a different game than O'Reilly does and it's the game Ellis wants. O'Reilly fit well when the USWNT's strategy focused around direct soccer and pure athleticism, but Ellis, since taking over as coach, has emphasized a more fluid and creative approach. Technical players who can switch positions and slowly break down defenses are much more appealing to Ellis.

Even so, there's something strange about a USWNT roster without O'Reilly. She's been a mainstay over the years and reliable veteran, whether as a starter or as a substitute. But now, O'Reilly is ready to embrace a new role as a practice player.

"I know HAO is disappointed that she's not going to be in the 18, but I know she's going to help us being successful down there," Ellis said. "With these players, you don't know if they want to be alternates. You hope they do. With Heather, I said, 'Are you prepared for this role?' and she said, 'For sure, of course.'"

O'Reilly posted a heartfelt message to fans after the squad was announced, lamenting that she missed the roster but vowing to help the team however she can, even as an alternate.

"In the 230 games that I have played for the USWNT so far, I have done it with my whole heart, with every ounce of me, regardless of the role, to help us win. Whether I was a starter, or a substitute, or even the times that I did not see the field," she wrote. "...And next month, I will travel to Rio with the team as an alternate. Once again, whatever I need to do to help the U.S. win, I will do with my whole heart."

From the O'Reilly everyone has gotten to know over the past 14 years, the one who is famous for her intense "game face," no one would expect anything less.

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