Key takeaways

• US sportsbooks reserve the right to limit or close accounts at their discretion. DraftKings' New Jersey terms say it can close an account "for any reason or no reason."

• Massachusetts regulators reviewed operator data and found that winning bettors had their limits cut while losing bettors had theirs raised. On average, 0.64% of the state's sports betting accounts were limited as of December 10, 2024.

• Massachusetts now requires sportsbooks to tell bettors within 48 hours when they've been limited and which markets the limit covers. Operators had to comply by June 1, 2026.

• Prediction markets such as Novig, Kalshi and Polymarket US match traders against each other. Federal rules require them to give access on impartial terms, so the practical cap on size there is liquidity in the order book.

Why sportsbooks limit arbitrage bettors

A sportsbook makes money on the margin built into its prices. An arber only bets when a book's price is off the market, which means every bet an arber places is one the book has priced worse than its competitors. Over enough volume, that account costs the book money no matter which side wins.

The UK name for the result is gubbing. A 2018 UK Parliament petition defined it as a bookmaker limiting "a customer to small stakes (often pennies)" and banning customers "from promotions or closes accounts." In the US the same thing happens without the slang, and it usually shows up as a lower maximum stake on a market rather than a closed account.

What the sportsbook terms allow

The legal basis sits in each operator's terms. Two examples from the largest US books:

• DraftKings' New Jersey terms of use: "DraftKings may also suspend or close your Account at any time in DraftKings' sole and absolute discretion, for any reason or no reason." The Michigan terms use the same wording.

• FanDuel's Iowa house rules: "FanDuel Sportsbook reserves the right in its sole discretion, to refuse, limit or cancel any wager or series of wagers."

BetMGM and Caesars publish house rules state by state too, and the version for the state you bet in is the one that governs your account.

What Massachusetts found

Massachusetts has studied limiting in public, with operator data. The Massachusetts Gaming Commission held a roundtable on the practice on May 21, 2024. DraftKings, FanDuel, Caesars, Fanatics and ESPN Bet declined to attend, and DraftKings said that taking part "would necessarily involve the disclosure of DraftKings' confidential risk management practices."

The commission then reviewed operator data itself. The minutes of its September 30, 2025 meeting record the staff finding: "players who demonstrated a tendency to win had their limit decreased and players who demonstrated a tendency to lose had their limit increased." Commission staff put the average share of limited accounts across operators at 0.64% as of December 10, 2024.

That review led to an amendment to 205 CMR 238.30, which the commission adopted 5-0 on February 26, 2026, with operators expected to comply by June 1, 2026. Operators in the state now need procedures "to provide timely notice to a patron that their wagering activity has been limited, including a specific explanation for the attachment of the limit(s) and identification as to which market(s) are so limited." The commission set "timely" at 48 hours. Books in the state can still limit an account, and the bettor now gets told which markets and why.

What tends to trigger a limit

Sportsbooks don't publish their criteria, so this part comes from risk-management vendors and people who've worked inside books. These are the signals they describe:

• Beating the closing line. Bets that consistently get a better price than where the line closes are the strongest sign of a sharp account.

• Bet timing. Bets placed seconds after a price goes stale elsewhere look like they came from a scanner.

• Stake patterns. Odd amounts such as $47.32 and stakes sized exactly to an arb split stand out.

• Only taking off-market prices. An account that never bets at the consensus price doesn't have any recreational action to offset the sharp bets.

• Promotion-only activity. Accounts that only show up for boosts and bonuses get flagged with the same tools.

How arbers keep accounts open longer

No habit keeps a winning account open indefinitely at a house sportsbook. A few slow the process down:

• Round stakes to whole numbers. The stake sizing guide shows what rounding costs in profit.

• Bet some markets at normal prices, not only the off-market leg.

• Spread action across more books so no single account carries all of it.

Opening a second account, or one in someone else's name, breaks sportsbook terms and costs more than any arb is worth when the book finds it.

How prediction markets handle winning accounts

Novig, Kalshi and Polymarket US are federally regulated as designated contract markets (Polymarket US through QCX LLC, designated in July 2025), and they match traders against each other instead of taking the other side themselves. The operator earns fees or nothing at all on a trade, so a sharp customer doesn't cost it money the way one costs a sportsbook.

The CFTC's rule for these markets, 17 CFR 38.151, requires "impartial access to its markets and services," with access criteria "applied in a non-discriminatory manner." Novig's own rulebook, filed with the CFTC as Ludlow Exchange, commits to access that is "impartial, transparent, fair and non-discriminatory."

These markets cap size with thresholds that apply to every account:

• Kalshi and Novig both use position accountability levels set contract by contract. Several of Kalshi's 2026 sports contract filings set the level at $25,000 per strike, per member.

• Polymarket US caps a single market buy at $1,000,000.

• On all three, an order only fills against orders already on the book. A thin market fills partly or at a worse price, so liquidity decides how much an arb can carry.

That's the case for putting one leg of an arb on a prediction market. With Novig or Kalshi on one side, only the sportsbook leg carries the risk of a limit.

Account limit questions

Is it legal for a sportsbook to limit a winning bettor?

Yes. Operator terms allow it, and Massachusetts, which has written a rule on it, requires notice and leaves the practice itself alone.

Will a limited account get its limits back?

No sportsbook publishes a process for restoring limits. In Massachusetts, the notice rule at least tells you which markets are limited.

Do prediction markets limit winners?

Their rulebooks require impartial access, and size caps such as position accountability levels apply to every account above the threshold. The practical constraint is liquidity on the book.

Does arbitrage betting break sportsbook terms?

Placing bets on both sides at different books doesn't break a rule by itself. Books can still limit an account they don't want, which is the point of the discretion clauses above.

Size your arbs before you place them

Use the arbitrage calculator to size both legs and see the worst-case profit after rounding, and check how a stake cap on one leg changes the other.