Nobody reasonable could say that Kris Bryant has disappointed in the majors. Hitting .287/.401/.468 with 1.8 WAR already in just under two months of play, Bryant has performed in the majors about as expected based on his minor league résumé. Bryant mania aside, however, he is only one of the prominent rookies this year called up not just to get experience in the majors, but to make a real impact in pennant races right now. And there are more to come.

One of the most important lessons that the Moneyball mindset has spread around baseball has little to do with statistics, but simply with the basic rules of how MLB finances are structured. Namely, that prospects are incredibly valuable. While this was always known, modern franchises place even more value on prospects, with blockbuster-type trades, such as Baltimore's pickup of Adam Jones, Chris Tillman, George Sherrill, Kam Mickolio and Tony Butler for a single season of Erik Bedard, becoming harder to pull off. You see the consequences of this in the increased tendency of top players to be traded more than a year before free agency, like Jeff Samardzija to Oakland and Zack Greinke to Milwaukee, in order to grab bigger packages.

With more focus being placed on top prospects, greater expectations come with the territory. The Astros called up Carlos Correa and Vincent Velasquez not to get their beaks wet in the majors, but to make the Astros better right now. Are these win-now expectations justified? Let's run 2015 rest-of-season ZiPS for the call-ups of the past month and for players who could conceivably be called up (and if unlikely to be called up, those who should be).

Carlos Correa

Preseason projection: .247/.311/.357

Current rest-of-season projection: .252/.315/.384

There weren't a lot of questions surrounding Correa coming into the season, with most of the uncertainty being when he would be ready to play in the majors, not if. While Houston was smart not to jump the gun and put him on the roster on Opening Day -- his highest minor league level was two months of high-A ball -- the Astros were open to letting him push his way onto the roster. And that's just what he did, hitting .385/.459/.726 in his month of Double-A play and putting up a .794 OPS for Fresno. Is he going to be a star? At this moment, probably not. But league-average shortstop performance is crucial for a team that lost its Opening Day shortstop, Jed Lowrie, to a thumb injury that's likely to cost him at least half a season. With the Astros' playoff hopes realistic, Correa is a far better option than muddling through with what they have.

Vincent Velasquez

Preseason projection: 5.21 ERA, 8.4 K/9, 4.3 BB/9

Current rest-of-season projection: 4.68 ERA, 8.8 K/9, 4.0 BB/9

If Correa rocketed to the majors this season, Velasquez set a new Kessel Run record. Keith Law's No. 56 prospect coming into the season, Velasquez had a very short track record given a wide variety of injuries (don't worry, no elbow or shoulder problems). ZiPS was understandably skeptical of a pitcher with no upper-minors experience, and while Velasquez still doesn't have a lot, his five starts in Corpus Christi were extremely impressive, with 37 strikeouts against only nine walks in 26 1/3 innings. Given the lack of quality at the back of the Astros' rotation -- they've intentionally given starts to Roberto Hernandez this season -- there's a line of thought to see if they can catch lightning in a bottle for a second time this year (the first being Lance McCullers so far).

Joey Gallo

Preseason projection: .209/.289/.450

Current rest-of-season projection: 220/299/451

Gallo, more than any prospect in baseball, represents that cool, retro, Three True Outcomes guy we haven't seen as often since offense dropped off considerably several years ago. Except in Texas, with the cross-state Astros also featuring a few of these types. Gallo may be the most extreme player of the type, and the trend has continued in the majors with a .531 slugging percentage through Thursday's games and strikeouts in nearly half his plate appearances. If not for the lack of the sweet 1980s Brewers unis and the lack of the even sweeter blonde mullet, I'd assume that the Rangers had signed Rob Deer. With the Rangers showing far more of a pulse the past month than it appeared they were capable of at this point, getting some power from Gallo while Adrian Beltre's out with a thumb injury is a lot more important.

Eduardo Rodriguez

Preseason projection: 4.33 ERA, 6.5 K/9, 3.2 BB/9

Current rest-of-season projection: 4.23 ERA, 6.5 K/9, 2.7 BB/9

Boston's Eduardo Rodriguez (2-0, 0.44) has held opponents to a .116 batting average in three starts. Jim Rogash/Getty Images

Twenty years ago, the Red Sox called up Vaughn Eshelman for a couple of spot starts and he proceeded to throw 13 scoreless innings. So there are some natural comparisons to Eduardo Rodriguez, who has allowed just one run in his first three starts. Those comparisons would be wrong. Rodriguez was a serious prospect coming into the season -- No. 29 by Law, No. 30 by ZiPS -- and his major league starts have been legitimately dominating, with a strikeout an inning. Coming back to earth is inevitable, but despite what you would think from some of the tone around Boston's disappointing season, the team remains alive in a mediocre AL East. Boston has been trying to get some nice surprise in the rotation, and Rodriguez is the first one this season. It also goes to show how organizations can make the most of lousy seasons; without the Red Sox disappointing last year, there's no way they flip Andrew Miller for a prospect down the stretch.

Players to come

Byron Buxton

Preseason projection: .251/.315/.386

Current rest-of-season projection: .255/.314/.410

If not for injuries that dogged Buxton in 2013-2014, we might have already seen him in the majors. Coming into the season, the Twins most wanted to see a big number by games played next to Buxton's name, and they've received that with 2012's No. 2 overall pick playing in 57 games already for Chattanooga. And he's performing the way the team wanted, with a .489 slugging percentage buoyed by a ridiculous 12 triples and a 20-2 SB-CS ratio. Patience made sense for the Twins coming into the season, given that the team didn't look very good. I still don't really see the Twins as a real contender come August, but given that they are currently near the top of the division, it makes sense to get the best team they can on the field quickly. Buxton may benefit from more minor league time, but the best Twins team includes Buxton at this point, with Minnesota getting a .615 OPS out of left fielders and a .592 from center fielders this year.

Julio Urias

Preseason projection: 3.77 ERA, 9.2 K/9, 4.5 BB/9

Current rest-of-season projection: 3.68 ERA, 9.4 K/9, 4.2 BB/9

Urias is unlikely to be called up soon, due to both the fact that he's currently out due to eye surgery and the Dodgers' insistence that he would stay on the farm in 2015. But let's say Urias is back to form around the All-Star break and the Giants are still nipping at the team's heels. How long can the Dodgers really resist calling up such a phenomenal talent? Hyun-Jin Ryu and Brandon McCarthy are out for the season. Brett Anderson has a precarious health record that leaves the team relatively thin after Clayton Kershaw and Zack Greinke, even if Mike Bolsinger continues to pitch well. Getting Cole Hamels or Johnny Cueto would not be an inexpensive proposition. If push comes to shove, I think we will see Urias this year.

Andrew Heaney

Preseason projection: 3.84 ERA, 7.8 K/9, 2.7 BB/9

Current rest-of-season projection: 3.85 ERA, 7.8 K/9, 2.9 BB/9

Don't be fooled by his relatively high ERA for Salt Lake; his FIP stands at 3.01 this season, an impressive number in the still notorious hitters' league that is the PCL. Heaney was a last-minute demotion to the minors after he essentially lost a rotation spot with a weak spring, but he was always a candidate to come back. Most non-Hector Santiago starters have disappointed this season for the Angels, and the team's going to need to get performance somewhere if it is to have a realistic AL West shot.

Francisco Lindor

Preseason projection: .244/.294/.358

Current rest-of-season projection: .249/.305/.355

White it was not surprising that Jose Ramirez's woeful .487 OPS resulted in a trip back to Triple-A, it was surprising that Francisco Lindor wasn't the replacement. A projected .660 OPS is hardly exciting, but remember that MLB shortstops are only at .672 in 2015, so just on offense Lindor's a major league shortstop right now. But offense isn't the main reason to like Lindor, it's just the side order to the main course, his plus defense, something Cleveland sorely needs. The Indians want to continue get back into the race, right? Add up Lindor's offense and defense, and he's the team's best shortstop right now. At the very least, have some mercy for poor Corey Kluber with the 3.53 ERA and 2.30 FIP.

Tyler Glasnow

Preseason projection: 4.09 ERA, 9.9 K/9, 5.5 BB/9

Current rest-of-season projection: 3.99 ERA, 10.0 K/9, 5.4 BB/9

Like Urias, Tyler Glasnow is also currently out due to a non-arm injury, this one a sprained ankle. The Pirates are playing it safe with Glasnow, given the risk that any kind of leg injury can affect a pitcher by changing his mechanics, which can have a negative effect on the stats and, in the worst case, increase the risk of an arm injury. But when he's back, if he continues to pitch well, the Pirates may be in an interesting quandary in August. Their rotation isn't an obvious problem, in contrast to a few of the teams on this list, but Glasnow seems to be a good candidate to get the classic Earl Weaver treatment and break into the majors as an impressive power arm in the bullpen. The Pirates aren't running away with any playoff spot, so each win is likely to be darn important in September.