The season has had its share of challenges for the Nationals. Every team faces these things, but not every team is considered a contender. With struggles and injuries come attention. And rookies.

It’s not just third baseman-turned-second baseman Anthony Rendon; there have been a slew of recent additions to the big-league pitching staff. One man’s trouble is another’s opportunity. Four times over.

In recent weeks (or days) three pitchers have made their major league debuts for the Nats. A fourth pitcher — one with big league experience — is also rejoining the squad and possibly will pitch in a Washington uniform for the first time.

Xavier Cedeno (Associated Press)

Xavier Cedeno was let go by the Astros. That’s not exactly a great introduction, but Houston is like any other franchise — it’s a numbers game. Cedeno does have some time in The Show, and he’s left-handed…and healthy.

He got off to an awful start for the Astros this April, which merited a roster move. In his case it was off the 40-man. Plucked off waivers and assigned to Triple-A Syracuse after a single day with the Nats. Cedeno settled down enough in the minors to get the call prior to Thursday’s rain out (according to Adam Kilgore, Cedeno will remain with the club this weekend).

Along with settling down he’s been setting down hitters, at the rate of 13.2 per 9 innings, according to Baseball Reference. That won’t last but at least we can look back at his moderate success in 2012 and have some optimism again.

Cedeno doesn’t throw very hard, with an upper 80s fastball, a cutter (86), change-up (84) and a curveball (79). Cedeno mixes both four- and two-seam fastballs, although left-handers rarely see the four-seam variety. He throws a bit of everything to right-handed hitters but he’s basically sinker/cutter when he’s got the platoon advantage.

Cedeno will join a bullpen that has two rookies lurking about. Lower in seniority, these guys are up the ranks in velocity.

Ian Krol (Jonathan Newton / The Washington Post)

At 19 years old, Ian Krol was one of the best and youngest starting pitchers in the Low A Midwest League. After some arm problems in 2012 he was converted to relief. While it took him three years to advance from Low A to Double A, he skipped Triple-A. This is not unusual; the best, yet inexperienced arms are often in Double-A.

With a healthy arm and some life experience (good and bad) Krol has emerged as a promising reliever. With his low-ish armslot from the left-side, his 95 mph fastball has extra appeal. His curveball (80) has always been an impressive pitch but he may need to prove his change-up (87) can be effective to help him face right-handed hitters in the majors.

Erik Davis (Alex Brandon/Associated Press) Erik Davis (Alex Brandon/Associated Press)

Erik Davis made his big-league debut and threw harder than he did back in the 2010 Arizona Fall League. He’s older, not coming off a full season and has converted to relief. Caveats aside, 94 mph is still a nice number when 89 was our other data point. Davis was a starter in the Padres system when he was exchanged for Alberto Gonzalez. The Nats moved Davis to the bullpen in 2012 and since then he’s been striking out more than one batter per inning in the minor leagues. At 26 years old, he certainly didn’t have the prospect status Krol still possesses, but he was effective against the more seasoned batters in Triple-A.

Krol’s southpaw delivery and ability to throw strikes certainly ranks him higher on the “will stick around” board than Davis. But Davis isn’t exactly wild and should be given a good, long look, especially with all the recent injuries and demotions.

(Jonathan Newton / The Washington Post)

Nate Karns was called up from Harrisburg to take Ross Detwiler’s turn in the rotation. Turn has turned into turns. Karns will make his third big-league start this weekend against the Mets. He’s made it into but not out of the fifth inning in his first two turns. He went from 3 strikeouts and 2 walks against Baltimore to 6 and 1 against Atlanta, effectively earning a third start.

Striking guys out shouldn’t be too rare an occurrence for Karns. With a 94 mph fastball (two- and four-seam) his best secondary pitch is his knuckle curve (85). He also throws a change-up (86) but he’s got a better whiff rate with his four-seam fastball than his change-up. That’s just about nine innings of work, so it’s not something to be worried about, but it isn’t something to be impressed by in that regard.

Karns will be given a chance to gain experience and solidify himself as rotation depth. Krol seems like the guy most likely to stick around, given his skill set. If nothing else, the past two months have shown the need for depth, so it won’t hurt to become familiar with all four of these guys.

Harry Pavlidis is the founder of Pitch Info. Follow him on Twitter: @harrypav.