They are the Minor Leaguers, who are not on the 40-man roster and did not receive an invite to big league camp, but have come over from Minor League camp to help fill in when needed.
While the playing time might not be great -- a few innings for a position player, an inning for a pitcher -- the opportunity to make an impression is.
"You get to lay your eyes on them and kind of start your book on them, start to create your history with them," D-backs manager Kirk Gibson said.
Those first impressions can last a long time.
Adam Eaton, who is expected to be the team's starting center fielder and leadoff hitter this year, first got his chance as a Minor League fill-in a few years ago and homered in his first at-bat.
"You're on cloud nine when you get that first at-bat," said Eaton, ranked by MLB.com as the D-backs' No. 5 prospect.
No one in recent memory has made as much of an immediate impression as Jon Griffin did last spring.
The first baseman came into a night game against the Rockies last year and in his first at-bat blasted a home run that landed on top of the batter's eye in center.
"The only guys I've seen hit the ball there are him and Buster Posey," Eaton said.
Getting called over from the Minor League side of the complex can be a bit overwhelming at first. And while Griffin looked composed, inside he was nervous.
"They told me to get in there, and I jumped up in the wrong spot to begin with," Griffin said. "I was on deck and it wasn't my turn, so I went back in. It was an awesome experience. It was pretty surprising, too."
Griffin was mentioned in Gibson's postgame news conference, and the story of his titanic blast spread quickly.
"I went back to my locker after the game and my phone was just blowing up," Griffin said. "I don't even think the game was televised either. It was pretty crazy."
Griffin was drafted in 2011 and had spent that summer with Rookie level Missoula, where he hit .295 with 18 homers.
Last year, he started at Class A Visalia and also saw time in Double-A Mobile. His performance during the 2012 regular season is what earned him a non-roster invite to big league camp this year, but that doesn't mean that Spring Training at-bat didn't have an impact.
"When you look back at his year and you see his numbers and what he did, you can kind of look back to that day and know that the processes were right in sending him, he performed well and there's no doubt it had an impact on his confidence," D-backs farm director Mike Bell said.
When the big league staff determines that it will need some extra players for a Cactus League game, either Gibson or one of his coaches will call over and tell the Minor League staff what positions they need coverage at. If it's a pitcher, they'll let them know how many innings of coverage they need.
As for who actually ends up going over, that's up to Bell and his staff.
"We do put a lot of thought into that," Bell said. "A lot of it you worry about where they're at as far as maturity. Can they handle it? Are they going to put too much pressure on themselves? Is it going to affect them negatively?"
There are times the players don't actually get into the game, but just sitting on the bench surrounded by Major Leaguers and the coaching staff is a learning experience, and there are things the staff picks up on as well.
"You want to expose them to where they want to go," Gibson said. "It will intimidate some, others will cherish it, but you have to go through it, and we aim to make them more comfortable the next time they're here. We like to do that. It's a good opportunity for them."
Gibson smiled when asked about people remembering the Griffin homer after the D-backs played the Rockies in the first game this spring and Griffin got an at-bat.
"The Rockies remembered that, too," Gibson said. "He saw a bunch of sliders."