SANTA CLARA, Calif. -- Before Kendrick Bourne ever signed with the San Francisco 49ers as an undrafted wide receiver out of Eastern Washington, he already knew that making the 53-man roster would be an uphill climb.

Bourne also knew that for him to get where he wanted to go, his lift ticket would come from his ability to play special teams as much as, if not more than, what he could do catching passes.

So when Bourne found himself lining up at gunner for the first time at the team's open practice on Aug. 5, he couldn't help but feel a little overwhelmed.

"I saw the first double-team I was going to go against and I was pretty nervous," Bourne said. "I didn't know how I was going to get off the line. I didn't know what technique I was going to use and I'm totally new to this."

Forget a "Welcome to the NFL" moment, this was a "Welcome to Life on the Fringe of an NFL Roster" moment. It's something that Bourne and many others like him go through every preseason. One NFL personnel executive recently estimated that at any point in an NFL training camp, there are between 46 and 50 roster spots already sewn up. The rest are up for grabs in heated competitions at positions like receiver, running back, linebacker and in the secondary.

And while the work that those battling for those jobs do on offense or defense is part of the equation, it's on special teams where jobs are ultimately won and lost. For those who truly embrace the often-thankless job of running down kickoffs or punts, entire careers can be made.

Take Niners linebacker Dekoda Watson, for example. He arrived at Tampa Bay as a seventh-round pick in 2010. Stuck behind linebacker Quincy Black on the depth chart, Watson recognized right away that if he wanted to carve out a lengthy NFL career, he would have to do it with the game's third phase as a foundation.

Watson is now entering his eighth NFL season and makes it a point to shine light on that path for his young teammates.

"I tell them to take this serious, this is where you are going to earn your bones," Watson said. "This is where you can have a long career in the league. I have lived it. Obviously, you want to do more but you have got to do what you've got to do at that particular time."

As an added benefit of that kind of longevity, it's almost inevitable that a chance to contribute on offense or defense will also come along. Watson has played 837 defensive snaps and made 87 tackles in 89 games and seven starts.

For other players, like Arizona cornerback Justin Bethel, special teams contributions have actually led to a full-time starter's role. Bethel has started 10 games since coming into the league in 2012 but is poised to start opposite Patrick Peterson in 2017.

"Even though you know you want to make it on offense or defense and make an impact there, going out and making splash plays and showing the coaches that as long as you're in that phase, you can change the game with one play," Bethel said. "Show you can go out there and make those plays. That's the way to go out there and make the team. That's pretty much what happened to me. My third game, playing Oakland, I blocked an extra point, then blocked a punt and picked it up and ran it in for a touchdown. That changes the game. So if you can go out there and show that, that's the way to show the coaches that 'Oh yeah, we need this guy.'"

For players like Watson and Bethel, making that impact is a task made easier by extensive backgrounds on special teams dating to high school and college. Not all players battling for NFL jobs on special teams have played there much previously, however.

Before this training camp, Bourne hadn't played anything but receiver since his freshman year of college. Running back Matt Breida, another undrafted free agent, had played special teams only off and on in his freshman and senior seasons at Georgia Southern.

Considering that special teams require a little different mindset, it's not the easiest transition to make, especially at NFL speeds.

"You have just got to be a dog, man," Bourne said. "At gunner, sometimes you get double-teamed and that stuff is hard to get off the jam, with two guys on you. You have got to be a dog and have that mentality that you can't be stopped. And you have to have a motor."

"You have got to have a little bit of nasty in you," Breida said. "You want to go out there and be physical and fast every play."

For players like Bourne and Breida, any opportunity to get on the field is a chance to open some eyes. Both have done so while playing offense, particularly in the preseason opener against the Chiefs. Still, while Bourne has played only two snaps on special teams and Breida has played one in the first two exhibition contests, they're getting more extensive work there in practice.

That dichotomy puts coach Kyle Shanahan in position to try to mix and match players as much as possible so he has a more complete evaluation when it's time to trim the roster to 53 players.

"Most of the things we do in a preseason game is because we're just trying to figure things out," Shanahan said. "There's certain guys that we have a good feel of, and there's certain guys that we don't. There's certain areas that we're not sure because we can't replicate it the exact right way in practice so we have to do it in the game. There's some things that we can replicate in practice, so we don't even worry about it in the game. So we put other guys in those situations.

"I think special teams is one of the toughest things to replicate in practice because, yeah, you can be physical, especially through training camp when we have pads on and everything, but we're not tackling. We're not taking people to the ground. Especially when you get offensive guys who are playing special teams. Most defensive guys do know how to tackle, especially at this level. Offensive guys aren't always that way. They're not going to show you that they're good tacklers in practice because we're not going to risk getting one of our guys hurt. So those are the guys that you've really got to get opportunities in the game on special teams."

Shanahan said Wednesday he'd be open to getting players like Bourne more chances on special teams, especially given how he's performed on offense. As it stands, the Niners figure to keep five or six wide receivers. If someone like Bourne can prove himself a capable special teams player, he can elbow his way not only onto the roster but also onto the list of players active on game day.

"If you aren't one of those top guys, if you aren't No. 1, No. 2, if you're not a true starter and you can't help on special teams, it's very hard to make the team," Bourne said. "It's a trickle-down effect. It's a risk sometimes you take because some of those guys can be very good and they're only one play away from being a starter. The problem is they weren't activated that day because they couldn't help on special teams. So you've got to wait until next week to do it. Special teams is a big part of it. If everyone stays healthy, then you want to think all about special teams, because the backups will contribute on that."

Flashing back to that open practice and his first rep as a gunner on punt coverage, Bourne remembers attempting to squeeze between two blockers and chase down punt returner Trent Taylor. Bourne's lack of straight-line speed compared to other receivers doesn't hurt him much on offense because there are other ways to create separation. He has no such advantage when chasing a punt returner, so he has to make up for it by getting off blocks a step faster than speedier players.

"I don't know if I made the play, I was pretty close," Bourne said. "I got a hand on Trent, and so that kind of felt good, but it was definitely a wake-up, like, 'Man, this stuff is serious; it's not going to be easy ever.'"

But for players on the bubble trying to make it in the NFL, it will always be necessary.