Same-Match Stacking: The Risk That Wasn't
Analyzed within-match outcome correlation across 30K matches. Same-match bets are ANTI-correlated (-0.153) — they hedge, not concentrate. 56% of pairs split (one wins, one loses). All 3 capping policies worsen ROI. The 40-60u match swings in live trading are a stake-sizing artifact, not structural correlation risk.
Same-Match Stacking: The Risk That Wasn't
When a single match produces 2-3 losing bets, it feels like correlated exposure — one bad result wipes out 40-60 units. From 55 live bets, we saw Sheffield Wednesday vs Ipswich produce both a +28u Under win and a -20u AH loss on the same match. Portsmouth vs Derby produced three wins totaling +48u. Are we over-concentrated?
The Question
Should we cap bets per match? Keep only the highest-edge bet? Limit to one per market type? The fear: when a match goes wrong, the correlation between bets means we lose everything at once.
What We Found
Same-match bets are anti-correlated. Win/loss correlation = -0.153. More than half (56%) of same-match bet pairs produce split outcomes — one wins, one loses.
This makes intuitive sense when you look at the market pairs:
| Pair | Win Correlation | Split % |
|---|---|---|
| AH+OU25 | +0.008 | 49.6% |
| 1X2+AH | +0.029 | 47.4% |
| 1X2+OU25 | -0.012 | 49.0% |
| AH+AH | -1.000 | 100% |
| OU25+OU25 | -1.000 | 100% |
Same-type pairs (two AH bets or two OU25 bets on the same match) are perfectly anti-correlated: they're opposite sides of the same line. One is Over, one is Under. One is Home AH, one is Away AH. They literally cancel out.
Cross-market pairs (AH + OU25) show near-zero correlation. A team covering the Asian handicap doesn't predict whether the total goes over or under. These are approximately independent bets.
The overall stacking we observed in live paper trading — multiple bets on the same match all losing — is a small-sample artifact, not a structural pattern.
The Policies
We simulated four approaches on 50K out-of-sample bets:
| Policy | N | ROI | Sharpe | Max DD | Max Match Loss |
|---|---|---|---|---|---|
| Status quo | 49,917 | **-5.6%** | -0.438 | 2,787 | 4.0 |
| Cap-1-best | 11,352 | -7.2% | -0.255 | 826 | 1.0 |
| Cap-1-per-market | 27,876 | -6.6% | -0.318 | 1,852 | 3.0 |
| Cap-2-diversified | 22,674 | -7.0% | -0.306 | 1,601 | 2.0 |
Every capping policy makes ROI worse. Cap-1-best produces the "best" Sharpe (-0.255 vs -0.438) but that's because it takes 4.4x fewer bets — less exposure to a market that's currently net-negative across all markets blended. The paired bootstrap p-value is 0.49 — not even close to significant.
The Nuance
Cap-1-best consistently improves Sharpe across all walk-forward periods (train, val, test). This isn't because it's a better signal — it's because it reduces exposure. Taking 1 bet per match instead of 4.6 means less total loss in a system that's currently CLV-positive but ROI-negative.
This is a position-sizing observation, not a signal discovery. If the model were profitable (positive ROI), capping would *hurt* — you'd be leaving profit on the table. The capping "improvement" is entirely an artifact of ROI being negative.
The max single-match loss in the backtest is 4 units (4 bets at 1u each). The 40-60u swings in live trading come from 20u stakes, not from stacking. That's a bankroll/sizing decision, not a stacking policy.
What This Means
No production change. Keep all bets. The within-match anti-correlation is actually beneficial — when one bet on a match loses, another often wins, providing natural hedging.
If we want to reduce per-match exposure for bankroll safety, the answer is stake sizing (reduce per-bet stake when multiple bets exist on the same match), not bet elimination. But this is a risk preference, not an edge improvement.
What's Next
Match stacking is closed as a research thread. The bigger question remains the CLV→ROI gap. These two research projects eliminated "thin edges" and "correlated stacking" as explanations, confirming that the gap is driven by model calibration and market structure — which is where the solver tuning and market routing work is focused.