These 5 players have opened eyes in April

It's early enough in the season that some numbers can still feel very odd, like Mookie Betts hitting .244 and Aaron Nola posting a 6.84 ERA. Then again, the three best players in baseball so far have been Cody Bellinger, Christian Yelich, and Mike Trout. Aaron Judge has the best hard-hit rate in the game. Byron Buxton is 2019's fastest runner. Kevin Kiermaier has been the best defensive outfielder. Some numbers really do matter already.

That's really what's interesting at this time of the year, anyway. Which numbers are noise -- and which are trying to tell you something you didn't know? Let's investigate a few hot starts to try to find out.

When we did this just over a year ago in April 2018, we identified the hot starts of Josh Hader, Adam Ottavino, and Brandon Nimmo as being so impressive that they couldn't be written off as mere small-sample luck, and all three ended up having tremendous seasons. We also pointed out how great Rick Porcello's start had been. Can't win 'em all.

There are more than five lesser-known players having starts that demand attention, obviously. You don't need us to tell you that Pete Alonso's massive power is for real. We can't list every reliever having a great start in their first eight innings. These are the five that stand out the most, at least at this juncture. We'll revisit this next month for five more.

1) Christian Walker's 99th percentile hard-hit rate (61.2 percent)

Walker, a first baseman, has always been stuck. Drafted by Baltimore in 2012, he was blocked by Chris Davis, back when Davis was still a star. From there, he went briefly to Atlanta (where he was never going to play ahead of Freddie Freeman), then Cincinnati (Joey Votto) and finally Arizona (Paul Goldschmidt). He went through all four teams in the span of about six weeks during Spring Training in 2017, then spent the majority of 2017-18 in Triple-A Reno, bashing 50 homers and popping up every so often to crush Clayton Kershaw.

Goldschmidt was traded to St. Louis this year, but Walker still wasn't given the first base job, since third baseman Jake Lamb was expected to shift across the diamond to serve as the strong side of a platoon. (On Feb. 21, Walker had "a chance" to make the roster.) Lamb started three of the first four games, then went down with a quad injury. Walker has started all but two games since. He might never give it back.

Walker, after a home run on Monday, is hitting .347/.413/.722. It's one of the ten best lines in baseball.That won't last, obviously, but he's currently got the fifth-best hard-hit rate in the game, behind only big-time sluggers Anthony Rendon, Judge, and Joey Gallo. Walker was always considered a powerful bat, we just didn't know if he could do it in the Majors. So far, so good.

2) Robert Stephenson's 99th percentile Expected Weighted On-Base Average (.167)

A quick Expected wOBA primer: It's a Statcast metric based on quality of contact (exit velocity and launch angle) and amount of contact (strikeouts and walks). The Major League average is .323.

You've heard this story before. Stephenson was a first-round pick in 2011 and was routinely a Top 100 prospect for years afterward, but he could never put it together at the highest level. In 22 starts over parts of three seasons, he had a 4.77 ERA. He spent time in Triple-A in each year from 2015-18. Late last season, the Reds gave up on Stephenson as a starter. He'd be in the bullpen full-time -- if he made the roster, which was no guarantee until Matt Wisler was the final cut of camp.

You might say it's made a difference. Stephenson has pulled off the intriguing combination of having a 96th percentile strikeout rate (38.1 percent) and a 94th percentile hard-hit rate (21.7 percent). Put all that together, and he's been the fourth-best pitcher in baseball in the early going, among those who have faced 25 batters.

It's not hard to see what's happened. His velocity has ticked up a little, but the move to the bullpen has allowed him to mostly drop his curve and changeup, while massively upping his slider usage. It had been clear for some time that the slider was a weapon, and the fastball was not. As pitchers like Ottavino have shown, it's perfectly fine to go with a secondary pitch as your primary pitch, if it's good enough. For Stephenson, it might be good enough.

Robert Stephenson and the slider of doom: pic.twitter.com/BHitW09XlI

— Mike Petriello (@mike_petriello) April 22, 2019

3) Max Fried's 99th percentile curveball movement and production

Fried isn't unlike Stephenson in that he was a former first round pick (No. 7 overall in 2012 by the Padres) who has taken something of a winding path, being traded to Atlanta in 2014 in the Justin Upton deal and missing all of 2015 due to Tommy John surgery. Fried got into 23 games (nine starts) for the Braves in 2017-18, but was pushed to relief last year and made his first two appearances of 2019 out of the bullpen as he waited for the fifth starter's turn to arrive.

That might have been a good thing -- “I’m not going to lie, going to the bullpen is something that helped me a lot with my mentality," he told MLB.com's Mark Bowman earlier this month -- and Fried has now allowed two runs or fewer in each of his four starts, for a 1.48 starting ERA.

He won't keep that up, because 18 strikeouts in those 24 1/3 innings is below average. But the curve, which had long been showing up on all those long-ago scouting reports, is for real, to the point that Cleveland manager Terry Francona compared him to Blake Snell after Fried shut down the Tribe on Sunday night.

Fried's curve has 93rd percentile spin, and it has the third-most drop among curveballs. It's also the third-best curve in 2019 based on expected outcomes, behind only Corey Kluber (who throws a breaking ball that's more like a slider than anything) and Aaron Sanchez. What that means is that he's allowed just a .111 average and a .148 slugging on the pitch, while collecting 10 whiffs.

It's a dominant hook. It looks like this.

4) Jorge Polanco’s long-running breakout in progress

It’s easy to forget now, but once upon a time, Polanco was a back-end Top 100 prospect who made it to the big leagues before his 21st birthday. He barely played in his first three seasons – just 78 Major League games from 2014-16 -- but then he looked like he was on the verge of a breakout, hitting a scorching .316/.377/.553 over the final two months of 2017. Of course, his 2018 was sidetracked before it ever began due to an 80-game suspension, and his solid enough .288/.345/.427 after his return was somewhat lost in the midst of a disappointing Twins season.

Polanco is only 25 years old, and after a four-hit game in Monday’s 9-5 win over Houston, his line now sits at .392/.452/.716. It is very legitimately one of the best starts in Twins history. There’s no expectation that he’ll hit .392 all year, and he won’t, but there are signs of real improvements here, from the huge jump in hard-hit rate (up to 44 percent from 28 percent) to the continuing decrease in ground-ball rate (down to 22 percent from 39 percent) to being more aggressive on the first pitch (a career-high 23 percent swing rate) while still keeping his strikeout rate better than the Major League average.

Put another way: Since Aug. 1, 2017, Polanco has hit better than Manny Machado, Bryce Harper, Francisco Lindor or Kris Bryant. He’s done it in fewer plate appearances, and there’s no way to look past the suspension that cost him half a season. But despite how long he’s seemingly been around, Polanco is still the same age as Byron Buxton -- and he’s leading a first-place Twins team.

5) Niko Goodrum's huge hard-hit improvement

Speaking of former Twins prospects, Goodrum was a second-round Minnesota pick back in 2010, spending years working his way up the chain before making a brief 11-game cameo in 2017. He signed with the Tigers as a non-roster player for 2018 and hit a league-average .245/.315/.432. It was fine. He was fine.

So far this year, he's been considerably more than fine, hitting .279/.380/.508 (134 OPS+), but the most interesting thing here is how much harder he's hitting the ball. Last year, Goodrum's hard-hit rate was 35.4 percent, or roughly league-average. This year, it's up to 52.2 percent, which is the fourth-largest jump (among those with 100 batted balls last year, and 30 so far this year) behind George Springer, Rendon and Willy Adames. As FanGraphs recently detailed, this is being paired with a huge uptick in pull percentage, as well as this incredible sentence: "It’s also a mix that looks like Jose Bautista’s breakout 2010."

We won't go quite that far, though it's worth noting that Goodrum also ranks incredibly well in running speed, with a 91st percentile mark that's A) Top 30 and B) faster so far than Whit Merrifield or Victor Robles. He's hitting the ball harder. He's pulling it more. He's hitting fewer grounders, down from 45 percent to 37 percent. Put all that together: His 95th percentile expected wOBA of .437 is 16th in baseball.

It won't stay that high, probably. But perhaps we should have paid more attention when Goodrum hit a 99.8 MPH Luis Severino pitch out at Yankee Stadium last August.

Dating back to 2017, it was one of only nine homers hit off pitches coming in at 99.8 MPH or harder. It's incredibly impressive -- just like the start to Goodrum's season.