Mariners vs Athletics Prediction, September 12, 2026 | Under 9.5
Bryan Woo vs Gage Jump at Sutter Health Park
Published September 12, 2026 · MLB Prediction Data Lab
The posted total is 9.5. A naive add of season run rates (3.96 for Mariners, 4.37 for Athletics) gets you 8.33 combined runs. That is not the bet. The bet is that Bryan Woo and Gage Jump plus Sutter Health Park pull the night below that baseline. Partitioning each starter's own earned-run rate across expected innings and handing the remainder to each club's season staff rate returns 9.31 projected earned runs.
This is the largest stake on today's card. The other unders the same night load on the same run-environment factor; size the card as one bet, not seven independent shots. Full board: MLB picks today.
The listed matchup
Seattle Mariners (69–79) at Athletics (60–88), Sutter Health Park, Sacramento. Bryan Woo, a right-hander, is listed for the visitors. Gage Jump, a left-hander, is listed for the home club. Void the play if either listed starter is scratched.
| Side | Listed starter | Record | Park |
|---|---|---|---|
| Mariners | Bryan Woo | 69–79 | Sutter Health Park |
| Athletics | Gage Jump | 60–88 | Open, grass |
The two starters, measured per batter faced
Rate statistics expressed per nine innings reward pitchers who work deep. Expressing them as a share of batters faced removes that distortion. Bryan Woo has faced 633 hitters. Gage Jump has faced 425.
| Starter | BF | K% | BB% | K−BB | K/BB | Pitches/BF |
|---|---|---|---|---|---|---|
| Bryan Woo | 633 | 25.0 | 5.2 | 19.7 | 4.79 | 3.78 |
| Gage Jump | 425 | 24.9 | 10.6 | 14.4 | 2.36 | 4.03 |
| Starter | W-L | ERA | IP | WHIP | K/9 | BB/9 | HR/9 | Opp AVG |
|---|---|---|---|---|---|---|---|---|
| Bryan Woo (R) | 11-9 | 4.03 | 156.1 | 1.06 | 9.10 | 1.90 | 1.04 | .224 |
| Gage Jump (L) | 6-10 | 5.12 | 96.2 | 1.49 | 9.87 | 4.19 | 0.93 | .266 |
Bryan Woo sits at a 4.03 ERA with a 1.06 WHIP and 33 walks in 156.1 innings. Gage Jump sits at a 5.12 ERA with a 1.49 WHIP and 45 walks in 96.2 innings. Walks stabilize faster than earned runs, so the walk column is the more trustworthy August reading.
Direction inside the season
Season aggregates hide the last month. These are the prior starts, excluding today's outing so the table does not leak a result into a published prediction.
| Bryan Woo — last starts | IP | ER | K | BB | H | HR | Pitches |
|---|---|---|---|---|---|---|---|
| 2026-08-11 | 5.0 | 0 | 5 | 1 | 3 | — | 92 |
| 2026-08-16 | 6.0 | 2 | 5 | 1 | 3 | 2 | 75 |
| 2026-08-26 | 4.0 | 6 | 5 | 1 | 5 | 2 | 76 |
| 2026-09-01 | 6.0 | 1 | 7 | 1 | 5 | 1 | 99 |
| 2026-09-06 | 8.0 | 0 | 9 | 2 | 1 | — | 102 |
| Gage Jump — last starts | IP | ER | K | BB | H | HR | Pitches |
|---|---|---|---|---|---|---|---|
| 2026-08-14 | 5.1 | 3 | 1 | 4 | 3 | 1 | 101 |
| 2026-08-20 | 4.0 | 5 | 3 | 3 | 8 | 1 | 86 |
| 2026-08-25 | 6.1 | 2 | 9 | 2 | 3 | — | 94 |
| 2026-08-31 | 4.1 | 7 | 2 | 3 | 6 | 1 | 91 |
| 2026-09-06 | 4.0 | 2 | 7 | — | 6 | — | 82 |
The run environment, before the starters
Mariners have scored 586 runs in 148 games (3.96 per game) with a .683 OPS. Athletics have scored 647 in 148 (4.37) with a .723 OPS. The pitching staffs have allowed 4.47 and 5.63 runs per game.
| Club | Record | R/G | OPS | Staff ERA | Staff WHIP | RA/G |
|---|---|---|---|---|---|---|
| Mariners | 69–79 | 3.96 | .683 | 4.22 | 1.25 | 4.47 |
| Athletics | 60–88 | 4.37 | .723 | 5.33 | 1.49 | 5.63 |
Reassembling the buckets
Bryan Woo averages 5.79 innings per start. Gage Jump averages 5.09. Weight each starter's own earned run average across that length, then hand the remainder of the nine innings to his club's season staff rate. That is a conservative relief proxy — it mixes rotation and bullpen — and it is stated as a limitation, not hidden.
| Side | Starter IP | Starter ERA | Relief IP | Staff ERA | Projected ER |
|---|---|---|---|---|---|
| Mariners (Bryan Woo) | 5.79 | 4.03 | 3.21 | 4.22 | 4.10 |
| Athletics (Gage Jump) | 5.09 | 5.12 | 3.91 | 5.33 | 5.21 |
| Combined | 9.31 |
A combined 9.31 projected earned runs against a 9.5 total. Unearned runs are ignored. Neither starter hits his average length every night. The opposing lineups are not in the formula; they sit in the table above.
The park
Sutter Health Park is listed at 330 feet to left, 380 feet to left center, 403 feet to center, 380 feet to right center, 325 feet to right, on grass, open at 24 feet above sea level with a listed capacity of 13,416. Park dimensions do not decide a total by themselves. They decide whether a walk plus a ball in the air becomes two runs or a long out.
Where this reading is weakest
The season run rates do not want this number. Combined they sit at 8.33 against a 9.5 total, a gap of -1.17 runs that the starters and the park have to close. Bryan Woo also allows 1.04 home runs per nine, and one three-run ball turns a low-event night into a push or a loss.
What would falsify it
A start from either pitcher that ends before the fifth with a pitch count above 95, or a walk total of four-plus from Gage Jump, is the cleanest failure signal. That is how a 9.5 total gets away: free baserunners, an early bullpen, and a second time through a lineup that already scores 4.37 runs a night on the higher side.
The position
Athletics/Mariners Under 9.5 at -110, 2 units. A price of -110 implies a 52.4% break-even. Grade it against this published number. If a listed starter is scratched, the play is void.
- Athletics/Mariners Under 9.5 -110 · 2u
Who is on the mound?
Bryan Woo for Mariners. Gage Jump for Athletics. Those names come from the MLB probable-pitcher feed, not from a guessed rotation.
Why use batters-faced rates instead of ERA?
Earned run average is a counting result. Strikeout and walk rates as a share of batters faced describe the process that produced it, and they stabilize on a smaller sample. Bryan Woo at 19.7 points of K−BB separation versus Gage Jump at 14.4 is the comparison ERA hides.
How is the pick graded?
Against the published price, on the public record. Pending is not a win. Today's full card lives at a stable URL: mlb-picks.html.
Pick, odds, and unit size come from the BetLegend daily tracker. Probable starters, season rates, and venue facts are from the MLB Stats API. Educational analysis. 18+ only. 1-800-GAMBLER.