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MLB Prop Bets: Seattle Mariners vs Athletics (April 21, 2026)

The Athletics (12-11) face the Seattle Mariners (10-14) at T-Mobile Park on Tuesday at 9:40pm (ET). Let's take a look at the MLB Prop Bets for the matchup. Jacob Lopez is the probable pitcher for the Athletics, while Luis Castillo is the probable pitcher for the Mariners. The Mariners are favored to win at -171, while the Athletics are at +141. The total runs line is set at 7.5, with OVER at -108 and UNDER at -112.

  • The Athletics (-149) have a 12-11 Run Line record this season, while the Mariners (+123) hold a record of 11-13.
  • The Athletics have a 12-10-1 O/U record this season (meaning 12 games have gone over the total runs line, 10 have gone under and one has resulted in a push). The Mariners have an 11-13-0 O/U record.

Scoring Insights

  • The Athletics are averaging 4.2 runs per game this season (18th in the league). Comparatively, the Mariners are averaging 3.9 (24th).
  • In the field, the Athletics are allowing 5.0 runs per game this season (23rd in the league), while the Mariners are allowing an average of 3.8 runs (7th).

Let's take a look at how these teams perform in some other key statistical areas.

Batting Insights:

Batting Average

  • Looking at their batting averages this season, the Athletics are at .234 (ranking 15th in the Major leagues), while the Mariners are batting .218 (28th).

Home Runs

  • In terms of total home runs this season, the Mariners have hit 23 (T14th in the Major Leagues). Meanwhile, the Athletics have managed 23 (T14th).

Runs Batted In

  • Finally, looking at their runs batted in, the Athletics have recorded 95 RBIs to rank 17th in the MLB this season. Comparatively, the Mariners have recorded 91 RBIs to rank T19th.

Pitching Insights:

Earned Run Average

  • The Mariners have one of the strongest earned run averages this season, sitting at 3.33 (3rd in the Majors), while the Athletics are at the opposite end of the scale with an ERA of 4.78 (25th).

Strikeouts

  • Turning our attention to total strikeouts, the Athletics have recorded 191 this season, ranking 15th in the MLB. Meanwhile, the Mariners rank 12th for total strikeouts, recording 200.

Opponent Batting Average

  • Opponents are batting an average of .250 against the Mariners this season (24th in the Major Leagues). Comparatively, the Athletics' opponents are at .245 (22nd).

First Innings Moneyline

  • Here are their first innings moneyline records in 2026.
    Total Home Road Favorite Underdog Neutral Last 10
    Athletics 1-11-11 1-5-4 0-6-7 1-3-1 0-8-10 0-0-0 1-6-3
    Mariners 8-6-10 7-4-4 1-2-6 8-5-7 0-1-3 0-0-0 6-1-3

Lead After Three Innings

The Athletics are +124 to lead after three innings, while the Mariners are -160.

  • Here are their records after the first three innings in 2026.
    Total Home Road Favorite Underdog Neutral Last 10
    Athletics 7-12-4 2-6-2 5-6-2 0-4-1 7-8-3 0-0-0 3-6-1
    Mariners 10-8-6 8-5-2 2-3-4 8-7-5 2-1-1 0-0-0 6-4-0

NRFI/YRFI

The NRFI market is paying -135 and the YRFI is paying +105.

  • The NRFI is 11-12 in Athletics games this season. The Mariners have an 8-16 NRFI record.

Last Time They Met

The Athletics recorded a 6-4 victory over the Mariners at T-Mobile Park yesterday. Carlos Cortes dominated at the plate in that matchup, notching 1 home run, 3 singles and an RBI.