MLB · Wednesday, Sep 23 · Matchup
Four back with five to play, Arizona take their season to Coors Field
The Diamondbacks need to win out and get help. They send Merrill Kelly and a 5.00 ERA into the thinnest air in baseball, against a Rockies rookie who gave up six earned runs in this ballpark a week ago.
Diamond Panther Desk writer, MLB
First pitch
8:40 PM ET / 5:40 PM PT
Wednesday, Sep 23
Ballpark
Coors Field
Rockies
Probable starters
Merrill Kelly vs Mason Adams
AZ, COL
Kalshi, both sides
60¢ vs 41¢
AZ, COL
What tonight decides
Diamondbacks
83-74
4.0 back in the wild card · 5 games left
Rockies
57-100
30.0 back · eliminated
Five games left, four back in the wild card. Arizona need to win out and get help.
Colorado were eliminated weeks ago. They are 32-47 at home and playing for next year.
That gap in motivation is real, and it is also the oldest trap in September baseball. The club with nothing to lose swings freely. The club that needs it presses.
Games back from the MLB standings, read Wed, Sep 23, 3:15 PM PT.2 Games left is arithmetic from the record. No elimination number is printed: two reads of that endpoint disagreed on it, so this page states only what both agree on.
The two arms
Merrill Kelly RHP #29
Diamondbacks
Mason Adams RHP #38
Rockies
| AZ | COL | |
|---|---|---|
| ERA | 5.00 | 5.09Worse |
| HR/9 | 1.61 | 2.35Worse |
| Innings, last 3 starts | 5.0 | 4.2Worse |
Kelly has not been the same pitcher this year: a 5.00 ERA, a 1.47 WHIP and 28 home runs in 156.2 innings.
That last number is the one that matters tonight. 1.61 home runs per nine, and Coors is the last place you want to bring it.
He has also stopped going deep. Two of his last three starts ended before the fifth was out, at 91 and 80 pitches to get there.
Full pitching line
9-14 · 28 starts · 156.2 IP · 1.47 WHIP
6.38 K/9 · 3.96 BB/9 · 1.61 HR/9 · .270 against
Last three starts
- Sep 16 vs Miami · 4.2 IP, 7 H, 3 ER, 2 BB, 9 K · 91 pitches
- Sep 11 vs Texas · 4.1 IP, 2 H, 1 ER, 3 BB, 3 K · 80 pitches
- Sep 4 at Houston · 6.0 IP, 7 H, 3 ER, 0 BB, 4 K · 94 pitches
Adams is a rookie, but he is not a mystery any more. Five starts, 23 innings, a 5.09 ERA.
The relevant one was a week ago, in this ballpark, against San Diego: 4.1 innings, eight hits, six earned runs.
Hitters are batting .299 against him and he has walked 4.70 per nine. Arizona will see pitches.
Full pitching line
0-1 · 5 starts · 23.0 IP · 1.65 WHIP
9.00 K/9 · 4.70 BB/9 · 2.35 HR/9 · .299 against
Last three starts
- Sep 16 vs San Diego · 4.1 IP, 8 H, 6 ER, 3 BB, 1 K · 84 pitches
- Sep 11 at Detroit · 5.0 IP, 2 H, 1 ER, 3 BB, 5 K · 77 pitches
- Sep 5 vs St. Louis · 4.2 IP, 8 H, 3 ER, 1 BB, 7 K · 78 pitches
Season lines and the start log from MLB’s player feed, read Wed, Sep 23, 3:15 PM PT.2 The innings-per-start row is arithmetic from that same log, most recent starts first.
How the two sides line up
| AZ | COL | |
|---|---|---|
| Record | 83-74 | 57-100 |
| Last ten | 5-5 | 2-8 |
| Streak | W3 | L2 |
| Runs for | 700 | 729 |
| Runs against | 696 | 911 |
| Run diff | +4 | -182 |
| Away / home | 38-38 | 32-47 |
| One-run games | 28-21 | 17-25 |
Every figure in this table, records included, comes from one dated MLB standings read, Wed, Sep 23, 3:15 PM PT.2 An undated read of the same endpoint returns both clubs a game behind these numbers; this page does not use it, and does not mix the two.
Coors Field plays bigger and thinner than anywhere else in the sport. The ball carries and the outfield is enormous.
The numbers say it plainly: Colorado have scored 729 runs and allowed 911. That spread is the ballpark, not the teams.
It is the single biggest reason a 57-100 club is priced as a live home underdog.
Who is swinging
Diamondbacks
- CGabriel Moreno.310 AVG · 15 HR · .871 OPS
- RFCorbin Carroll.240 AVG · 22 HR · .803 OPS
- 3BNolan Arenado.250 AVG · 28 HR · .786 OPS
- 2BKetel Marte.249 AVG · 22 HR · .747 OPS
- SSGeraldo Perdomo.257 AVG · 9 HR · .730 OPS
Rockies
- 1BTJ Rumfield.298 AVG · 15 HR · .837 OPS
- CHunter Goodman.243 AVG · 39 HR · .834 OPS
- LFJake McCarthy.295 AVG · 15 HR · .824 OPS
- CFCole Carrigg.272 AVG · 10 HR · .797 OPS
- LFMickey Moniak.242 AVG · 23 HR · .771 OPS
Hunter Goodman has hit 39 home runs for a last-place club. He is the one bat here that changes a game on its own, and Kelly has given up 28.
Arizona’s best hitter by OPS is their catcher. Gabriel Moreno is at .310, and Adams has let opponents hit .299 off him.
Top five by OPS among hitters with at least 300 plate appearances, from MLB’s team hitting feed, read Wed, Sep 23, 3:15 PM PT.2 The 300 plate-appearance floor is ours and is stated here because it changes the list: without it both sides are led by players with fewer than fifty trips to the plate. This is a season ranking, not tonight’s batting order, which is not posted until first pitch.
Who is not playing
Diamondbacks 5 out
- A.J. PukInjured 60-DayLeft ulnar collateral ligament surgery recovery
- Andrew SaalfrankInjured 60-DayLeft labrum repair surgery
- Cristian MenaInjured 60-DayRight shoulder strain
- Ryan ThompsonInjured 60-DayStrained lower back
- Tyler LocklearInjured 60-DayFractured right thumb
Rockies 6 out
- Willi CastroInjured 10-DayLeft heel inflammation
- Kris BryantInjured 60-DayLumbar degenerative disk disease
- Chase DollanderInjured 60-DayRight elbow strain
- McCade BrownInjured 60-DayRight shoulder inflammation
- Pierson OhlInjured 60-DayReason not published
- Welinton HerreraInjured 60-DayLeft elbow inflammation
Three of Arizona’s five unavailable players are bullpen arms, which matters on a night their starter may not finish the fifth. Colorado’s most recent loss is Willi Castro, out since September 2.
Injured list from MLB’s dated 40-man roster feed, read Wed, Sep 23, 3:30 PM PT.2 The roster feed carries the list type only, never a body part; every reason here is the wording of the club’s own transaction. Where a transaction does not say, this page says so rather than guessing.
What the market says
The Diamondbacks are 83-74 against the Rockies at 57-100, and the market agrees without much conviction: 60¢ against 41¢. A price in that range is the crowd saying the better club should win and often does not.
| Side | Record | Bid / ask | Last | Contracts traded |
|---|---|---|---|---|
| Diamondbacks | 83-74 | 59¢ / 60¢ | 60¢ | 28,111 |
| Rockies | 57-100 | 40¢ / 41¢ | 41¢ | 1,000 |
Kalshi series KXMLBGAME, event 26SEP232040AZCOL, read Wed, Sep 23, 2026, 5:20 AM PT.1 You pay the ask to buy and take the bid to sell, so a round trip costs more than one column suggests.
Run the numbers
These are the prices we read at Wed, Sep 23, 2026, 5:20 AM PT, not numbers we typed in. Pick a stake and the panel counts the contracts it buys at 60¢, the fee on the way in, what a sell at your target returns if it fills, and what the whole position costs if Diamondbacks lose. Nothing here places an order and nothing is saved.
Trading it: the case each way
The case for AZ at 60¢
Arizona are the better club by 26 games and the only side here with a reason to be.
They are 28-21 in one-run games and they come in on a three-game run. That is the record you are paying for.
Adams has given up six home runs in 23 innings. Put that in Coors and the runs should come.
The case for COL at 41¢
Sixty cents is a lot to pay for a starter with a 5.00 ERA at altitude.
Colorado have actually scored more runs this year than Arizona: 729 to 700. Their problem is the 911 they have allowed, and tonight the pitching is a wash.
If Kelly is out in the fifth again this becomes a bullpen game a mile above sea level, and three of Arizona’s five injured players are relievers.
We post a call where we think a price is wrong, and every call is graded on Kalshi’s own trade history, fees counted, win or lose. Our position on this game, if we took one, is in the rail beside this article. How we lock and grade
Reading the price
A contract pays $1.00 if that side wins and nothing if it loses, so the price is the crowd’s probability with the house’s cut on top. At 60¢, the crowd says 60% on Diamondbacks. At 41¢ it says 41% on Rockies.
Those two add to 101%, not 100%. The extra 1 points are the spread between buying and selling, and it is what the market charges to take either side. It is the first thing to subtract before deciding a price is cheap.
Merrill Kelly starts for Diamondbacks and Mason Adams for Rockies. A starter is the single biggest thing in a one-game price, which is why a team can be better all season and still be the underdog tonight.
How we grade
If the desk posts a call on this game it goes up before first pitch with the buy price, the sell target and what happens if the target never fills, and it is graded on Kalshi’s own trade history with both fee legs counted, win or lose. A miss stays on the record next to the wins. How we lock and grade
The result page for this game is already up and will carry the final, the line score and every call once Kalshi settles the market. See the result page
Sources
Read Wed, Sep 23, 2026, 5:20 AM PT. Prices move after that; this page is not updated in place.
- Kalshi public markets API, series KXMLBGAME, event 26SEP232040AZCOL: both sides, bid, ask, last and contracts traded. kalshi.com
- MLB schedule feed: records, first pitch, ballpark and probable starters. statsapi.mlb.com
PM Countdown is not affiliated with or endorsed by Kalshi, MLB or any club. Prices are the market’s own. Diamond Panther is a PM Countdown desk pen name.
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