Welcome to the MLB Star Power Index -- a weekly temperature reading that tells us which players are owning the baseball conversation right now. While one's presence on this list is often a positive, it's not necessarily a good thing. It simply means that you're capturing the baseball world's attention for one reason or another. The players listed are in no particular order. Thanks to Brad Botkin and our NBA compadres for letting us borrow the concept. 

George Springer
TOR • CF • #4
BA0.320
R39
HR16
RBI40
SB4
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George Springer has been among the the hottest batsmen in baseball of late. At this writing, the Houston center fielder owns a slash line of .320/.400/.651, which comes to an AL-leading OPS+ of 179. He also leads the AL in home runs with 16 (he was robbed of No. 17 against the Tigers on Wednesday) and total bases with 112. Throw in the fact that Springer is an up-the-middle defender who also runs the bases well, and you've got a complete threat and an early member of the AL MVP watch-list. 

Speaking of complete threat, let's watch Springer flash his excellence at the plate and his speed on the bases with one aesthetically pleasing inside-the-park homer: 

Hey, when you're accustomed to driving on two wheels you don't need to worry how the Chevelle handles corners. It says here that's Springer's best homer of the season. You may disagree on the grounds that the freedom to be wrong is an important freedom. 

Also notable is that Springer this season has played in every one of his team's games. That's notable because Springer has dealt with health issues throughout his career. In 2014, it was a major quad injury. In 2015 it was a concussion followed by a broken wrist. In 2017, it was a quad injury, and last year it was a thumb sprain. If Springer wants to finish in the top of the AL MVP balloting for the first time in his career, then he's going to need to continue producing at a high level and stay healthy. So far, he's checked both of those boxes. He's answered the bell every game, and he's been the best hitter on the best offense in MLB. 

Bryce Harper
PHI • RF • #3
BA0.220
R25
HR7
RBI25
SB1
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All right so Bryce Harper cracks the list this week for his defense and the ensuing discussion thereof. Consider not one but four instances of his work afield from the past few days: 

And: 

And: 

All right so that's a lot of good-looking work out there in right field, occasionally undertaken with a buccaneering disregard for walls. The effort is certainly there. We know, though, that just because a catch looks impressive doesn't mean that it was in fact a miracle snare or something close to it. Thanks to differences in range, one fielder's routine play becomes another's player hat-to-the-wind, wall-kisser of a catch. Peak Andruw Jones, for instance, had such incredible range and fly-catching instincts that he rarely needed to resort to theatrics.

As for Harper, his defense was a major uncertainty heading into his free agency. He's an across-the-board volatile performer whose value tends to swing pretty widely from year to year. Part of that is his defense, and that was especially the case in his walk year of 2018 with the Nationals. Harper last season put up some ugly defensive numbers -- ugly enough to sap much of his overall value and raise concerns about premature decline heading into free agency.  Ben Lindbergh of The Ringer did a deep dive into this subject, and he found some evidence that Harper was scaling back his defensive effort in the name of self-preservation. The color-television footage above suggests that Harper is no longer exercising such caution, which stands to reason given his $330 million contract (and given the idea that self-preservation in the field probably wouldn't play well in Philly). But what about the results?

Per Baseball-Reference, Harper's fielding has been worth minus-0.3 runs relative to replacement level. That's not good, but scaled to a full season it would be a substantial improvement over 2018, when Baseball-Reference tabbed him at a career-worse minus-3.2 runs. FanGraphs uses a different advanced defensive metric, and their estimations are much rosier. Ultimate Zone Rating (UZR), the FanGraps defensive stat of note in this instance, sees Harper as having been a substantial asset in the field. Indeed, relative to his positional peers Harper according to UZR has been one of the best fielders in baseball thus far in 2019. 

As for Statcast, they peg Harper thus far as a dead-average defender based on how he's converted his opportunities at the "catch probability" level. So that gives us three different estimations at three different points on the defensive continuum. 

The thing to remember is that defensive metrics can provide unreliable results, even across full seasons. So don't read too much into these quarter-season outputs. What we do know is that Harper is no longer holding back in the field. It's also safe to assume that he's been significantly better with the glove than he was last season -- that much all three systems agree upon. He's playing more shallow this season than he was in 2018, and he's improved both at coming in and going back on the ball. The positioning probably has something to do with that, and it may also be that his occasionally bothersome lower half is healthier thus far in 2019. 

Hyun-Jin Ryu
TOR • SP • #99
ERA1.72
WHIP.73
IP52.1
BB3
K54
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Hyun-Jin Ryu, as you can see above, has been outstanding thus far in 2019. Note in particular that jaw-dropping strikeout-to-walk ratio: 54 strikeouts against just three free passes. That comes a K/BB ratio of 18.00. The all-time record for K/BB ratio (among qualifiers)? That would belong to Phil Hughes, who with the Twins in 2014 put up a K/BB of 11.63. Ryu, obviously, is on pace to shatter that mark. 

Will he get there? The SportsLine Projection Model (@SportsLine on Twitter) tabs Ryu for 114 strikeouts and 20 walks over the remainder of the season. That would give him totals of 168 strikeouts and 23 walks ... so no. He's not likely to maintain the necessary clip, at least according to SportsLine. That stands to reason given that Ryu entered this season with a career K/BB ratio of 3.59. 

Ryu this season has swapped out a lot of curveballs in exchange for more cutters, and maybe that's a chance to his pitch mix that affords sustainable improvement at the command-and-control level. Speaking of which, the curve is the pitch that's typically the hardest to throw for strikes, and that's been the case with Ryu. Those changes are also not something that any projection system will pick up on. So it says here that, yes, Ryu will wind up setting the record in 2019. 

Edwin Jackson
ARI • SP • #36
ERA3.60
WHIP1.40
IP5.0
BB1
K2
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You'll note that Edwin Jackson in the thumbnail image above is wearing the combat headgear of the Oakland Athletics. However, those in the know know that Jackson now plies his trade for the Toronto Blue Jays. You see, not even our finest and most attentive widgets can keep up with the peregrinations of Edwin Darn Jackson. That brings us to this: 

HIlls be shaken: Mr. Jackson, as of his Wednesday start for the Jays, has now played for 46.7 percent of the league. That's a record -- i.e., playing for 14 different squadrons. What's more, the itinerant moundsman of note, who's been doing this since 2003, has pitched in 35 different ballparks. Thirty-five! No-longer-active venues in which he's taken the bump include the Metrodome, RFK Stadium, old Yankee Stadium, SunLife Stadium, Turner Field, and Qualcomm Stadium. The only active park he hasn't pitched in is SunTrust, new home of the Braves. But who wants to go there anyway. 

Edwin Jackson, foreman of 35 worksites and possibly counting.