Ten key players to watch in the second half

Manny Machado has become more disciplined at the plate, and the dividends are impressive. G Fiume/Getty Images

The second half is underway! There is no shortage of big storylines, and the July 31 trade deadline will prove even more interesting with so many teams still in the playoff chase. Most likely, however, it is not trades but players already on rosters that will decide the postseason teams. Here are 10 guys to watch in the second half:

Justin Verlander, Detroit Tigers

Just two seasons ago, the Tigers had one of the best rotations of the past 15 seasons. Their 23.1 FanGraphs WAR ranks fourth-best of any group of starters since 2000. The decline of the Detroit rotation has been rapid and ugly, even with David Price essentially replacing Max Scherzer this season. Although Price earned an All-Star trip with a terrific first half and Anibal Sanchez has been better lately -- he's 6-0 with a 2.86 ERA in his past seven starts -- the key to Detroit's playoff hopes might reside in former MVP and Cy Young Award winner Justin Verlander.

Verlander missed the first two months of the season with a triceps issue, and his early returns in five starts aren't positive. He's 0-2 with a 5.34 ERA, six home runs allowed in just 30.1 innings and a startlingly low strikeout rate of 13.5 percent, down from 25.8 percent in his 2011 MVP/Cy Young Award season. To put that decline in perspective, Verlander ranks 261st in strikeout rate among 289 pitchers who have thrown at least 30 innings in 2015. Sure, that includes relievers, but Verlander's demise from future Hall of Famer to bottom-of-the-rotation fodder is sad to witness. Is there a chance for a turnaround? I don't see signs of it, as his problems still result from the diminished velocity and effectiveness of his fastball. Check his wOBA allowed on his fastball through the years:

2011: .293

2012: .331

2013: .358

2014: .365

2015: .390

The Tigers are built to win now, with Price a free agent and Victor Martinez, Ian Kinsler and Miguel Cabrera all in their 30s. The Tigers are 8 1/2 games behind the Royals but just 3 1/2 out of a wild card. They need to remain close until Cabrera (calf injury) returns from the disabled list, and with J.D. Martinez on fire (10 home runs in his past 14 games) and Victor Martinez owning a .941 OPS since his return from the DL, that's possible. But they need Verlander to find a way to succeed if they're going to return to the playoffs for a fifth straight season.

Manny Machado, Baltimore Orioles

His improvement at the plate has turned him into the player who has the best chance of beating Mike Trout for MVP honors, especially if the Orioles can make the playoffs with a second-half surge like they had in 2014. His natural hitting style is different from Trout's; whereas Trout likes the ball down, Machado likes it up.

Machado's improvement has come from better plate discipline. His walk rate is up from 5.7 percent in 2014 to 9.9, which has led to a decrease in strikeouts. He is laying off pitches off the plate, which often got him out last year. Check out his numbers on pitches in the outer third of the strike zone (or outside):

2014: .228/.302/.272

2015: .245/.368/.445

In 2014, Machado didn't hit a single home run on a pitch located on the outer third of the zone. He has seven this year -- all to the opposite field. His swing rate has gone from 45.3 percent to 33.1 percent. He is smarter, he is stronger, and now he is a star hitter to go with his Gold Glove defense. Machado hit .365/.411/.635 in June. The Orioles need him to continue to carry the offense.

Yordano Ventura, Kansas City Royals

With the best record in the American League, the Royals are a good bet to make the playoffs -- FanGraphs gives them 84 percent odds to do so -- but they would love for Ventura to have a big second half and be the guy to start the first game of the postseason -- no offense to Edinson Volquez or Chris Young, the two reliable starters in what has otherwise been a shaky Royals rotation.

The good news is when you dig into Ventura's peripherals, he's pretty much the same pitcher as the past season, just with a higher ERA, due to a much worse left-on-base percentage. The bad news is his fastball has been hit much harder than IN 2014, with a .378 wOBA versus .327. His average fastball velocity has dipped from 96.8 mph to 95.8 mph. He is off the DL and presumably healthy, so let's see if he can get back into a 2014-esque groove.

Carlos Correa, Houston Astros

His first 33 games in the majors have been even better than expected, with a .275/.310/.500 batting line that includes seven home runs and 10 doubles. Maybe it's unfair to expect a 20-year-old to be a focal point of the offense, but if the Astros are to beat out the Angels or win a wild card, they need Correa to keep producing, especially with George Springer currently on the DL, Evan Gattis, Luis Valbuena and Jason Castro carrying sub-.300 OBPs, and Chris Carter hitting .185 with a .300 OBP. Correa's makeup is off the charts, but we'll see how he adjusts as pitchers attempt to exploit what has been an aggressive approach: swinging at 34 percent of pitches outside the strike zone.

Alex Rodriguez, New York Yankees

His second half got off to a good start, with a home run in Friday's win. At his best, A-Rod could always punish fastballs, and he's back to doing that. He is hitting .301/.411/.609 against fastballs, similar to what he did in 2009 (.296/.427/.593). He has played in 83 of the Yankees' 89 games. Can he stay healthy? Will he wear down after he turns 40 on July 27? Will he lead the Yankees back into the postseason?

Gerrit Cole, Pittsburgh Pirates

After seeing Cole up close at Monday's interview session during the All-Star break, I see a pitcher who not only has the numbers of an ace but also exudes all the qualities of an ace. He's smart, confident, poised and thoughtful, and as he becomes a bigger name to the casual fan, he is one of those players who should become one of the faces of the sport. With veteran A.J. Burnett a good bet to regress in the second half, the pressure will be on Cole to match his monster first half (13-3, 2.30 ERA). Lefties gave him a bit of trouble the past season, but not in 2015 -- they're hitting just .156 against his slider and slugging .269 against his fastball. The only question will be how he holds up as he approaches 200 innings for the first time in the majors.

Bryce Harper, Washington Nationals

Harper is hitting .338/.465/.701. Repeat: .338/.465/.701. His park- and era-adjusted wRC+ is 215, which is 12th all time since 1901. The only hitters who were higher: Bonds, Ruth, Williams, Hornsby and Mantle. We're in the midst of one of the greatest offensive seasons ever seen. Talk about carrying an offense. And considering the injury-marred seasons to Anthony Rendon, Ryan Zimmerman and Jayson Werth and the awful year from Ian Desmond, the Nationals have needed all that offense. Along with Arizona's Paul Goldschmidt, Harper has a chance at the Triple Crown. Will the Nats pull away from the Mets? If Harper continues to rake like this, I'd say yes.

Carlos Martinez, St. Louis Cardinals

He was one of the biggest surprises of the first half, as he went 10-3 with a 2.52 ERA. Not that he didn't have the stuff all along, but he wasn't dominant in relief the past season. And he seems to be getting better: In his past 10 starts, he has a 1.20 ERA and has allowed more than two runs just once (he allowed three). Batters are hitting just .203 with three home runs in that span. The command isn't always there, but Martinez's stuff is so good, he's kind of like one of those pitchers who is effectively wild. Like Cole, he has never spent an entire season in the rotation, but with the Cardinals and Pirates battling for the NL Central crown, it will be difficult to back off on his innings. Martinez (6-feet, 185 pounds) doesn't have the physical size of Cole (6-foot-4, 222 pounds), so we'll see how he holds up down the stretch.

Joe Panik and Brandon Crawford, San Francisco Giants

The middle infield pair made the All-Star team, and deservedly so. Both have added power -- Crawford ranks 11th in the NL in extra-base hits, while Panik has more than Troy Tulowitzki, Buster Posey or Justin Upton -- to go with their excellent defense. The Giants' homegrown infield has been huge because the rotation has been a weakness. Matt Cain and Jake Peavy have returned from the DL, but you don't know what to expect from them. The offense will have to lead the Giants back to the postseason.