MLB Alternate Run Lines and How They Pay

An alternate run line moves the standard 1.5-run MLB spread to another half-run number, and sportsbooks reprice both sides' odds to match how often games end at each margin.

DraftKings lists alternates from -5.5 to +5.5 in half-run steps on most games, under the alternate run line subcategory of its game lines, according to its MLB alternate run line board. The standard -1.5/+1.5 line stays fixed beside them.

The chosen number decides what margin a ticket needs and what it pays. Books price alternates with implied win probability models built on historical MLB scoring margins, according to Legal Sports Report.

Each half-run step adds or removes one exact final margin. A favorite moved from -1.5 to -2.5 no longer cashes on a two-run win. An underdog moved from +1.5 to +2.5 now cashes on a two-run loss.

The size of that margin sets the size of the price change. In an analysis of 800 MLB games, about 28% were decided by exactly one run and about 18% by exactly two, according to Betting for Baseball. The 18% covers two-run games won by either team, so only part of it moves any one bet.

Both sides reprice in opposite directions. A favorite at 5/6 (-120) on -1.5 might price at 7/4 (+175) or 2/1 (+200) on -2.5, while an underdog at 4/6 (-150) on +1.5 might tighten to 2/5 (-250) or 1/3 (-300) on +2.5, the same site said.

Further out the gap widens. Favorites at -2.5 or -3.5 can pay as much as about +350, and underdogs given +2.5 or +3.5 can cost as much as -700, an implied probability of 87.5%, according to SportsCapping.

Half-run alternates cannot push, because no game ends on a half-run margin. On a whole-number line, a final margin equal to the number settles as a push when no tie option was offered, under DraftKings house rules filed with the Massachusetts Gaming Commission.

Home favorites carry a structural cap. "If the home team has a one-run lead heading into the bottom of the ninth, they will not bat," Legal Sports Report wrote. Road favorites won by two or more runs 39% of the time against 27% for home favorites, according to Sports Betting Dime, which attributed the gap to that rule.

Hard Rock Bet priced ALCS Game 4 with the Rays at -115 and the Guardians at -105 on the moneyline, according to Rotowire. The run line was Rays -1.5 at +160 and Guardians +1.5 at -195, with a total of 6.5.

Those prices imply about 38.5% for the Rays to win by two or more and about 66.1% for the Guardians to stay within one run or win. The Guardians were reported to be planning a bullpen game with rookie Daniel Espino as a candidate opener. The alternate prices for that game are not in the data available for this article.

The same line carries different prices at different books. On Covers, Tampa Bay at -1.5 against Cleveland implied 37% to 39%, and Cleveland at +1.5 implied 64% to 67%. In a Milwaukee and Los Angeles game, Milwaukee at +1.5 implied about 60% and the Dodgers at -1.5 implied 40% to 41%.

Alternates also let a bettor flip the line and make the moneyline underdog the run-line favorite, according to DraftKings. DocSports priced a hypothetical Red Sox flipped line at +260 against a +160 moneyline. The flipped line breaks even at about 28%, the moneyline at about 38%.

DraftKings lists an Alternate Total Runs market beside alternate run lines. That market grades combined runs scored. An alternate run line grades only the margin between the two teams.

Two alternate tickets placed on opposite sides do not automatically form a middle. A -1.5 favorite paired with a +2.5 underdog wins both only on a two-run margin by the favorite, according to Betting for Baseball, which put that rate at about 18%. That figure counts two-run wins by either team, so it overstates the hit rate for any single pairing.

A bettor can convert each alternate price to its implied probability and compare it with how often games end at that margin. A price is only worth taking when the bettor's estimate of the margin beats the price's implied rate, which is the expected value test.

The grading rules differ by book. Circa Sports voids run line and alternate run line bets when the listed starting pitcher changes, according to its house rules. Circa carries suspended games over for 3 days. Major books including DraftKings commonly use a 36-hour window.

None of the sources say why DraftKings stops at 5.5 runs or why other books stop at 3.5 or 4.5. Every alternate is priced off the standard 1.5 run line, so reading the base price comes before reading the ladder.