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MLB Betting Odds, Picks & Predictions: Houston Astros vs. Seattle Mariners (Monday, Sept. 21)

MLB Betting Odds, Picks & Predictions: Houston Astros vs. Seattle Mariners (Monday, Sept. 21) article feature image

Lindsey Wasson//Getty Images. Pictured: Marco Gonzales.

Astros vs. Mariners Odds

Astros Odds -155 [Bet Now]
Mariners Odds +130 [Bet Now]
Over/Under 7.5 (-120/-110) [Bet Now]
First Pitch 9:10 p.m. ET

Odds as of Sunday night and via DraftKings. Get up to a $1,000 sign-up bonus at DraftKings today or see more offers and reviews for the best online sportsbooks.

The Houston Astros will look to improve upon their sixth-seed positioning in the playoff picture on Monday night against Marco Gonzales and the Seattle Mariners. The Astros’ lineup is finally healthy and trying to turn things around offensively after a poor couple of weeks at the plate. Meanwhile, the Mariners trail them by 2.5 games in the standings, so they need to take this series if they want to have a chance at making the playoffs. 

Advanced Stats Glossary

FIP or Fielding Independent Pitching measures what a pitcher’s ERA would look like if the pitcher experienced league-average defense and luck. xFIP  is a regressed version of FIP that adjusts or “normalizes’ the home run component based on park factors.

wRC+ or Weighted Runs Created Plus takes the statistic Runs Created and adjusts that number to account for critical external factors — like ballpark or era. It’s adjusted, so a wRC+ of 100 is league average, and 150 would be 50 percent above league average.

wOBA or Weighted On-Base Average is a catch-all hitting metric with more predictive value than on-base percentage. An average MLB hitter can be expected to post a .320 wOBA. xwOBA is a regressed version of wOBA that accounts for variables like park factors.

BaseRuns is a formula designed to estimate how many runs a team would be expected to score (or allow) given their underlying offensive (or defensive) performance. In other words, BaseRuns is a context-neutral run estimator used to evaluate teams. Major League average for an individual batter per game is 0.50 BaseRuns and a for a pitcher its 0.52 BaseRuns per inning.

Houston Astros

Houston has struggled offensively, accumulating a .309 wOBA and 98 wRC+. Those struggles have never been more apparent than the last two weeks, as the Astros have only a .247 wOBA and 55 wRC+, which is the worst mark in baseball over that time span. In fact, George Springer is the only Astro with a wOBA over .320.

Houston has also had a difficult time against left-handed pitching, ranking 17th in MLB in terms of wOBA. The Astros will have a tough matchup against Marco Gonzales, who has been one of the best righties in the American League West this year for the Mariners.

Astros Probable Starter 

Lance McCullers, Jr.

Projected & Actual Stats (via Fangraphs)

Pitch Arsenal (via Baseball Savant)

McCullers is starting to find his form after a rough start to the season. He missed all of 2019 due to Tommy John surgery, and it took him a while to find his command again. He’s lowered his xFIP all the way down to 3.94, but he is seemingly still having issues with his sinker and curveball.

Both pitches are allowing over .320 wOBA to opponents, and his sinker is generating a whiff rate of only 12.1%. His changeup has by far been his best pitch, allowing only a .232 average to opponents. Seattle has been pretty average versus righties this season, so McCullers has a good opportunity to keep his momentum going in the right direction.

Seattle Mariners

The Mariners have been below average offensively this season, checking in with a .303 wOBA and 94 wRC+. Rookie Kyle Lewis has been major positive for the Mariners this season, accumulating a .372 wOBA and 141 wRC+. While they started out as one of the worst offenses in baseball, they have turned things on in the second half of the season, hitting for the 16th-best wOBA compared to being in the bottom of five during the first half of the season.

Mariners Probable Starter

Marco Gonzales, RHP

Projected & Actual Stats (via Fangraphs)

Pitch Arsenal (via Baseball Savant)

Gonzales has been one of the best pitchers that nobody is talking about. His sinker has been fantastic so far this season, allowing only .189 wOBA on it. His secondary pitches have also been really effective, collectively allowing only .241 average to opponents.

Gonzales is having one of the best seasons of his career, and the reason for that has been his command. He has one of the lowest WHIPs in baseball at 0.90, mostly due to the fact that he has walked only five batters in 56.1 innings. The Astros have been horrible offensively as of late, so Gonzales has a good matchup on Monday night.


The Mariners have the worst bullpen in all of baseball, with a 5.01 xFIP. They traded away their best relievers at the deadline, and it has been a wasteland ever since. Meanwhile, the Astros have improved from their early season struggles and now have the 14th-best bullpen. So, Houston will have the advantage in the later innings during this series.

Projections and Pick 

Given how good Gonzales has been this season, I don’t think the Mariners should be underdogs in this game. However, since they have the worst bullpen in baseball, I am going to avoid taking them for the full game at all costs. So, I am going to back Seattle for the first five innings instead at +125 (DraftKings), and I would bet that up to +107.

Pick: Mariners First Five Innings +125

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