Cincinnati Reds vs Seattle Mariners Starting Lineup — Tuesday, Jul 21, 2026

Cincinnati Reds at Seattle Mariners (2026-07-21). Chase Burns vs Luis Castillo at T-Mobile Park.

Starters — Chase Burns has been the sharper profile overall with a 2.54 ERA, 1.11 WHIP, and 102.2 innings, backed by a strong 10.34 K/9. His 3.24 BB/9 is the main watch point, and his 1.05 HR/9 is manageable. Over his last three starts, he has allowed 10 earned runs in 17 innings, with one outing featuring six walks, so the recent trend points slightly up in volatility despite the season-long dominance. Luis Castillo enters with a 4.93 ERA, 1.37 WHIP, and 87.2 innings, with 8.32 K/9, 2.87 BB/9, and 1.23 HR/9. His last three starts were steadier, allowing 7 earned runs across 17 innings with only 3 total walks, and his recent trend is up after two cleaner outings following a rougher stretch.

Teams — Cincinnati has a .709 OPS and 414 runs, giving it a small edge in overall production. The Reds’ pitching staff has been less reliable, carrying a 4.60 ERA and 1.44 WHIP, and they are 4-6 over their last 10 games. Seattle has a .688 OPS and 410 runs, so the offense has been slightly less efficient but still close in raw scoring. The Mariners’ bigger team advantage is on the mound, where they own a 3.57 ERA and 1.17 WHIP. They are also 4-6 in their last 10 games, so recent form does not separate the clubs much. From a betting angle, this matchup sets up as Cincinnati bringing the more dominant starter and slightly better lineup output, while Seattle counters with the stronger overall staff support and home setting.