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The Emmanuel Rivera Trade

The trade improved both teams. Emmanuel Rivera has significant potential to improve.

Emmanuel Rivera plays in his first game as a Diamondback.
Emmanuel Rivera plays in his first game as a Diamondback.
Photo by Ron Schwane/Getty Images

The Diamondbacks traded away Luke Weaver for Emmanuel Rivera. Trading Luke Weaver was a bit of a surprise in the context that the Diamondbacks had some high impact players that were traded or might have been traded (like David Peralta, Ian Kennedy, and Christian Walker). Let’s look the Emmanuel Rivera trade.

The players will make an immediate Impact.

This view may be overly simplistic, but the trade immediately made both teams better. Basic reasons follow:

Royals: In July Luke Weaver had an ERA of 1.13 in 8 innings pitched for the Diamondbacks. He immediately makes their bullpen better. Prior to this season, Luke Weaver was a starter. If the Royals could quickly tweak Weaver and return him to a starter role, his value would greatly increase. In addition, the departure of Emmanuel Rivera frees up playing time for younger players Bobby Witt Jr (drafted first round in 2019) and Maikel Garcia (international signing in 2016).

Diamondbacks: Emmanuel Rivera is a right-handed batter who crushes left-handed pitching (especially in July). The Diamondbacks need him to balance their left-handed batters (Rojas, Thomas, Varsho, McCarthy, Smith, and Beer). In addition, the Diamondbacks can redeploy Weaver’s salary to areas of need.

The players may be near their peak performance.

This view could easily be wrong (it is definitely wrong in my view); both players are near their career peak performance. Possibly they will remain at their respective plateaus and then decline.

Luke Weaver. This month he turns 29 years old, no longer young for a pitcher. This season he moved from a starter role to the bullpen. His 4-seam fastball’s 94.6 MPH average velocity is a career high, but that peak is likely due to his new role as a reliever. For his 4-seam fastball, batters have a .362 expected weighted batting average (xwOBA), which is a career worst. In 2022, his 7.71 ERA with the Diamondbacks is a career worst.

In July, he achieved a 1.13 ERA. Was the improvement due to an adjustment in his pitching? Was the improvement due to lower pitch counts (26 pitches was his maximum in July)? Many things considered; he could be near his peak.

Emmanuel Rivera. He may have reached his career ceiling as a player drafted in the 19th round of the 2015 draft. His OPS+ was consistently been below average in the Majors (78 in 2021 and 91 in 2022 with the Royals). One caveat is that in his first 6 PAs for the Diamondbacks, his OPS+ was 109. Although it could be said that at 26 years old, Emmanuel Rivera has a couple years before reaching his peak, the Diamondbacks have many position players who have more room for growth (with 11 position players who have played this season and who are younger than Emmanuel Rivera). Relatively speaking, he is closer to his peak than many Diamondbacks position players. But the question is, “Has he peaked?”

Emmanuel Rivera has significant potential to improve.

This view is the optimistic view, supported by two things. First, he has not yet reached the potential he showed in the minors.

“He was originally a 19th-round pick in 2015 out of Puerto Rico, but the power he showed in Triple-A never translated to the big leagues, and his defense showed flashes but was inconsistent.” — Max Rieper, Royals Review of SB Nation, 1 August

Second, ignoring months with very little playing time, Emmanuel Rivera has only four months experience in the Majors. Almost certainly, he is still making adjustments.

What I especially like is that he could be a power hitter who drives in runs, very much improving the Diamondbacks. His potential for power hitting was shown by the following:

  • In 2022, his 8.4% barrels was better than Brendan Rodgers’ 7.9% barrels (which Baseball Savant showed as 50th percentile for the league on 6 August).
  • In 2022 with the Royals, his .028 homers per PA was good, but below my All-Star demarcation of .038 homers per PA.
  • In his first ten PAs as a Diamondback he hit a homer. Although ten PAs is a small sample size, his .100 homers per PA exceeded my All-Star demarcation.
  • On 5 August, I was pleased to see his eighth inning ‘laser’ line drive to left field, which setup Geraldo Perdomo’s go-ahead hit against the Rockies.
  • “I love the bat speed [of Emmanuel Rivera].” — Torey Lovullo

Let’s look at positives about Emmanuel Rivera.

Excellent batter against left-handed pitching & possibly July was a breakthrough month.

What he adds to the Diamondbacks is an infielder who hits very well against left-handed pitchers. It bears noting that in July his .345 wOBA against fastballs of right-handed pitchers was a hair above the league average.

“He is a good hitter. Period. But I think his strength is that he can go out and really smash left-handed pitching.” — Torey Lovullo

The following graph shows Emmanuel Rivera’s wOBA against left-handed pitchers. The biggest take-away is that in July, Emmanuel Rivera’s wOBA against left-handed pitchers was above the league average for each category of pitch (fastballs, breaking, and offspeed). Another take-away is that his results improved in 2022 compared to 2021. Data points with less than 10 swings have more uncertainty, which was shown with a bigger diamond and a pattern fill of the diamond.

Emmanuel Rivera. 2022 league averages were through 4 August. Data from Baseball Savant.

What if Rivera improved his performance against right-handed pitchers? Although that improvement could be too optimistic, with a different team (the Diamondbacks), a different coach, and a different venue, it remains a possibility. That improvement would open the possibility that in 2023 he could compete for opening day starter at third base. In the off-season, there were four AZ Snake Pit articles about candidates to play third base for the Diamondbacks (one, two, three, four). Perhaps Emmanuel Rivera will win the third base position in 2023.

Next, let’s look at swing efficiency. Swing efficiency is how often the ball is in play for each swing. For more information about Diamondbacks’ swings, see this AZ Snake Pit article . In general his swing efficiency was good against left handed pitchers. In July, he had a lower swing efficiency against offspeed pitches, but the reason is unknown.

Swing Efficiency is Balls in Play (BIP) divided by all swings (BIP + fouls+ foul tips + swinging strikes). Data from Baseball Savant.

Excellent defense at third base.

My view is that The Fielding Bible’s Defensive Runs Saved at third base showed his defense as above average. And he can play at first base, too. Defense details follow.

Before he was traded, Emmanuel Rivera had a positive 2 Defensive Runs Saved (DRS) per The Fielding Bible and a negative 4 Outs Above Average (OAA) (13th percentile per Baseball Savant).

The inconsistency in those statistics left me wondering if there was another way to look at the data. Where would Rivera rank in DRS per inning played (DRS/I)? Excluding players with less than 400 innings this season, Rivera’s positive .00424 DRS/I ranked as 9th best of 24 players. As a comparison, Josh Rojas’ negative .00341 DRS/I ranked as 16th best.

“I love the ability [of Emmanuel Rivera] to make plays defensively; he’s moving laterally very well.” — Torey Lovullo


The trade improved both teams by player performance and by freed playing time for younger players. Luke Weaver and Emmanuel Rivera had great results in July; Emmanuel Rivera made a breakthrough in smashing left-handed pitching. He has excellent potential to improve, especially as a power batter. His swing efficiency and bat speed are excellent. His defense at third base may be better than any current Diamondback. With excellent defense added to his excellent hitting against left-handed pitchers, potentially he will play third base for the Diamondbacks for five years. He would reach arbitration in 2025 and free agency in 2028.