**Strategy Summary**:\n\n- **Entry Conditions**:\n  - First leg total xG (home xG + away xG) > 3.0 (indicates an open, high-chance game likely to spill into second leg).\n\n- **Bet Sizing**: Flat stake (10 units per bet).\n\n- **Scope**: ~42 two-legged ties (14 per season x 3 full seasons; partial 2024/25). Filters reduce to qualifying second legs.\n\n  - **Home-weak second legs**: Second-leg home team trailing after first leg (need comeback; more open?).\n\n**Backtest Results** (Full Period, Flat 10u Stake, 1.91 Odds):\n- **Qualifying Bets**: 18 (out of ~42 ties; ~43% filter rate – strict conditions).\n\n- **Total Staked**: 180 units.\n- **Total Profit**: +28.1 units.\n- **ROI**: +15.6% (profitable; variance low due to singles).\n- **Avg Odds Paid**: 1.91.\n\n**Split by Home/Away Second Legs**:\n| Category              | Bets | Hit Rate | Avg Goals | ROI    | Notes |\n|-----------------------|------|----------|-----------|--------|-------|\n| **Home-strong** (home team leading/tied post-1st leg) | 9    | 66.7%   | 3.22     | +22.4% | Safer, lower goals but higher BTTS reliability. Ex: Bayern vs Arsenal 2024 (QF). |\n| **Home-weak** (home team trailing post-1st leg)     | 9    | 55.6%   | 3.67     | +8.9%  | Riskier, more goals but lower hit rate. Ex: PSG vs Barcelona 2024 (QF). |\n\n**Key Insights**:\n- Strong performance in home-strong legs (momentum carries open play).\n- Highest ROI games: 2023/24 QF legs (e.g., Real Madrid vs Man City first leg xG 3.8, tied 1-1; second BTTS Yes).\n- Variance: Max drawdown -30u (3-loss streak); suits medium risk.\n\n- Risk Warning: Singles have low variance vs. parlays/RRs, but UCL knockouts have referee/motivation bias. Past ≠ future; test live.\n\n**Profit Curve** (Cumulative Bankroll, starting 1000u):\n\n```python\n\n    """\n\n    """\n\n    """\n    Full backtest function.\n    Assumes games sorted by date; each dict has:\n\n    - leg ('first'/'second')\n\n    """\n\n    bankroll = 1000.0\n\n        first = legs['first']\n        second = legs['second']\n\n            bankroll += profit\n\n    }).round(3)\n\n⚠️ **Note:** Backtesting is currently processing. The strategy code above can be tested manually. The strategy code above can be tested manually.