As often happens with this column, a hot player shows signs of a potential breakout forcing fantasy players to look under the hood in order to determine its sustainability. This week leads us right to Austin Riley , the defending National League player of the week. During his hot stretch last week, Riley tied for the most home runs in the majors with six and run scored with nine while ranking second in RBI with 11. His .462 average, 1.308 slugging percentage and 1.772 on-base plus slugging percentage (OPS) led all major league hitters. 

While this appears to be a spike in production, Mark Bowman points out in his game recap on this past Sunday following a two-home run contest by Riley it's been a hot month or so: 

It's important noting he's a streaky player as alluded to in his quote above. This can be seen in his rolling game chart highlighting his weighted on-base average (wOBA), isolated power, contact rate and Z-Contact (in the strike zone) percentages: 

While it's terrific to see this stretch of dominance culminating in his huge power surge last week, it needs to be tempered. Especially given his varied results in terms of isolated power above. With this in mind, it's time to dive into his season as a whole. 

Through 48 games he's accrued 185 plate appearances with 27 runs, nine home runs, 21 RBI and a .312/.405/.535 slash line. So six of his nine home runs happened over the previous seven days. He owns a .402 wOBA with a .364 expected weighted on-base average (xwOBA) suggesting some migration to the mean lies in the offing. Presently his isolated power sits at .223, which represents a career best as does his 10.8 walk percentage. Despite the recent hot stretch his strikeout rate remains at 28.6 percent so his discipline remains a work in progress.  

According to Statcast, Riley's recorded 106 batted ball events with 14 barrels (13.2 percent), which ties his total from last year's spring in fewer events, with a 46.2 hard hit percentage and robust .472 expected weighted on-base average on contact (xwOBAcon). Part of the reason for believing some regression happens sooner rather than later, his .262 expected batting average (50 points below his actual) and a .491 expected slugging (44 points below his present slugging percentage). 

Hope lies in his reduced swing percentage, down 7.2 percentage points compared to last year along with a reduction in his chase rate. Despite growth in ground ball and fly balls, he's producing with fewer line drives. Any positive outcomes in terms of line drive rate could offset some of the pending migration to the mean. So track his batted ball data closely. Many view the Statcast indicators without diving deeper into the data, so keep this in mind then view his present chart and spray chart: 

His willingness to drive the ball to the opposite field this year may be a key to his progression as a hitter. He's pulling the ball less this year, hitting up the middle at a stable rate and increasing his opposite field percentage to 30.2 percent. Riley's also upped his solid plus barrel percentages to a combined 22.6 percent versus 15 percent in 2020. A positive development. 

Before leaving his plate discipline, here's his swing and take chart from 2021 courtesy of Statcast: 

Viewing his discipline metrics on Fangraphs yielded a lower swinging strike percentage (12.2 in 2021 versus 14.8 in 2020) and a drop of almost six percent in his O-Swing (outside the strike zone) percentage. His power and average may fluctuate throughout the season but it's the lower swing rates, especially outside the strike zone which insulates a potential breakout. Putting all of this into a bow, here's his rest-of-the-season projection sets:

This signals a realistic chance of Riley reaching his first 30 home run season with an average of .265-to-.275 possible. Right now, he's in the midst of a breakout but not willing to call it a full blown yet until the season ends. Everyone remembers his hot stretch during his rookie season followed by a complete cratering soon thereafter. Heed the discipline, profit on the power bursts and keep tabs on the recent developments fueling his results. He's on the precipice of a breakout and hoping it carries through the next four months. 

Statistical Credits:

ZiPS courtesy of Dan Szymborski

THE BAT and THE BAT X courtesy of Derek Carty