diff --git a/docs/strategies.md b/docs/strategies.md
index adee01be..bee5e184 100644
--- a/docs/strategies.md
+++ b/docs/strategies.md
@@ -52,6 +52,7 @@ only from `--both-sides`, side/kickoff cells, or `--fuzz-restarts`.
 | `press_trigger_flow` | competitive | `counter_flow`, but an all-in press when the ball is lost in our own third. |
 | `overload_press` | parked | 4-robot overload/switch attack + 1 block, built to outnumber tiki_taka's shadow line. |
 | `high_line_zone` | parked | Zone screen (`BlockShapeTactic`) + switch attack, built to deny tiki_taka 1v1s. |
+| `zone_split_shape` | experimental | `split_shape`'s tactics; the 4/1 possession split shifts one robot by the ball's third (3/2 building out from our own third, 2/3 when the ball is lost in theirs), near-ties keep the last split. |
 
 ## Latest results
 
diff --git a/utama_core/strategy/kernel_strategy.py b/utama_core/strategy/kernel_strategy.py
index 63881430..2d76e977 100644
--- a/utama_core/strategy/kernel_strategy.py
+++ b/utama_core/strategy/kernel_strategy.py
@@ -69,3 +69,7 @@
     _zone_flow_picker,
     build_zone_fluid_kernel_strategy,
 )
+from utama_core.strategy.zone_split_shape import (
+    _zone_split_picker,
+    build_zone_split_shape_kernel_strategy,
+)
diff --git a/utama_core/strategy/zone_split_shape.py b/utama_core/strategy/zone_split_shape.py
new file mode 100644
index 00000000..4e1b807c
--- /dev/null
+++ b/utama_core/strategy/zone_split_shape.py
@@ -0,0 +1,82 @@
+"""The `zone_split_shape` kernel strategy: `split_shape`'s two tactics with a split that reads the ball's third."""
+
+from __future__ import annotations
+
+from typing import Optional
+
+from utama_core.engine.context import TickContext
+from utama_core.engine.strategy import Strategy as KernelSchedulerStrategy
+from utama_core.engine.tactic import RobotId
+from utama_core.entities.game import Game
+from utama_core.motion_planning.src.common.motion_controller import MotionController
+from utama_core.strategy.pickers import (
+    ball_zone,
+    carrier_first,
+    friendly_closer_to_ball,
+)
+from utama_core.tactics.lead_and_support import LeadAndSupportTactic
+from utama_core.tactics.shadow_and_mark import ShadowAndMarkTactic
+
+
+def _attack_count(n: int, edge: Optional[bool], zone: str, prev_attack: Optional[int]) -> int:
+    """How many of `n` free robots attack.
+
+    With the ball: 4 of 5 in the middle and final thirds, but one fewer in our own third, so a
+    build-out from the back keeps cover. Without it: 1 of 5 when the ball is in our own or middle
+    third, but 2 when it is in their final third, so a robot stays up to win the ball back there.
+    A near-tie (`edge` None) keeps the previous count.
+    """
+    if edge is None:
+        if prev_attack is not None:
+            return max(0, min(n, prev_attack))
+        edge = False
+    if edge:
+        count = (n + 1) // 2 + 1
+        if zone == "own":
+            count -= 1
+    else:
+        count = n // 2 - 1
+        if zone == "final":
+            count += 1
+    return max(0, min(n, count))
+
+
+def _zone_split_picker(
+    game: Game,
+    free_robots: frozenset[RobotId],
+    prev_partition: Optional[dict[str, frozenset[RobotId]]],
+    available_tactic_ids: frozenset[str],
+) -> dict[str, frozenset[RobotId]]:
+    """`split_shape`'s possession split, shifted one robot by where the ball is. See `_attack_count`."""
+    ordered = carrier_first(game, free_robots)
+    if not ordered:
+        return {}
+    if "attack" not in available_tactic_ids:
+        return {"defense": frozenset(ordered)} if "defense" in available_tactic_ids else {}
+    if "defense" not in available_tactic_ids:
+        return {"attack": frozenset(ordered)}
+
+    prev_attack = len(prev_partition["attack"]) if prev_partition and "attack" in prev_partition else None
+    attack_count = _attack_count(len(ordered), friendly_closer_to_ball(game), ball_zone(game), prev_attack)
+
+    partition = {}
+    if attack_count > 0:
+        partition["attack"] = frozenset(ordered[:attack_count])
+    if attack_count < len(ordered):
+        partition["defense"] = frozenset(ordered[attack_count:])
+    return partition
+
+
+def build_zone_split_shape_kernel_strategy(outfield_robot_ids: tuple[int, ...]):
+    """`split_shape` with the split shifted by the ball's third of the pitch."""
+
+    def _build(motion_controller: MotionController) -> KernelSchedulerStrategy:
+        ctx = TickContext(motion_controller=motion_controller)
+        return KernelSchedulerStrategy(
+            tactics={"attack": LeadAndSupportTactic(), "defense": ShadowAndMarkTactic()},
+            partitioner=_zone_split_picker,
+            outfield_robot_ids=outfield_robot_ids,
+            ctx=ctx,
+        )
+
+    return _build
diff --git a/utama_core/tests/strategy/test_zone_split_shape.py b/utama_core/tests/strategy/test_zone_split_shape.py
new file mode 100644
index 00000000..398cfd6b
--- /dev/null
+++ b/utama_core/tests/strategy/test_zone_split_shape.py
@@ -0,0 +1,74 @@
+from types import SimpleNamespace
+
+import pytest
+
+from utama_core.entities.data.object import TeamType
+from utama_core.strategy.kernel_strategy import _zone_split_picker
+from utama_core.strategy.zone_split_shape import _attack_count
+
+FREE = frozenset({1, 2, 3, 4, 5})
+BOTH = frozenset({"attack", "defense"})
+
+
+@pytest.mark.parametrize(
+    "edge, zone, expected",
+    [
+        (True, "own", 3),
+        (True, "mid", 4),
+        (True, "final", 4),
+        (False, "own", 1),
+        (False, "mid", 1),
+        (False, "final", 2),
+    ],
+)
+def test_five_robot_split_by_possession_and_third(edge, zone, expected):
+    assert _attack_count(5, edge, zone, prev_attack=None) == expected
+
+
+def test_a_near_tie_keeps_the_previous_count_whatever_the_third():
+    assert _attack_count(5, None, "own", prev_attack=4) == 4
+    assert _attack_count(5, None, "final", prev_attack=1) == 1
+
+
+def test_a_near_tie_with_no_history_is_the_defensive_split():
+    assert _attack_count(5, None, "mid", prev_attack=None) == 1
+
+
+def test_counts_stay_within_the_robots_available():
+    assert _attack_count(1, True, "mid", None) == 1
+    assert _attack_count(2, False, "final", None) == 1
+    assert _attack_count(0, True, "mid", None) == 0
+
+
+def _game(ball_x, friendly_dist, enemy_dist, carrier=None):
+    distances = {TeamType.FRIENDLY: (3, friendly_dist), TeamType.ENEMY: (1, enemy_dist)}
+    return SimpleNamespace(
+        proximity_lookup=SimpleNamespace(closest_to_ball=lambda team_type_filter: distances[team_type_filter]),
+        my_team_is_right=True,
+        field=SimpleNamespace(half_length=4.5),
+        ball=SimpleNamespace(
+            p=SimpleNamespace(to_2d=lambda: SimpleNamespace(x=ball_x)), v=SimpleNamespace(x=1.0, y=0.0)
+        ),
+        friendly_robots={rid: SimpleNamespace(has_ball=rid == carrier) for rid in range(1, 6)},
+        enemy_robots={1: SimpleNamespace(has_ball=False)},
+    )
+
+
+def test_building_out_from_our_own_third_keeps_a_second_defender_back():
+    # my_team_is_right: our goal is at +x, so x = +3.2 is our own third.
+    partition = _zone_split_picker(_game(3.2, 0.2, 0.8, carrier=3), FREE, None, BOTH)
+    assert len(partition["attack"]) == 3 and len(partition["defense"]) == 2
+    assert 3 in partition["attack"]
+
+
+def test_losing_the_ball_in_their_third_keeps_a_robot_up():
+    partition = _zone_split_picker(_game(-3.2, 0.8, 0.2), FREE, None, BOTH)
+    assert len(partition["attack"]) == 2 and len(partition["defense"]) == 3
+
+
+def test_a_pinned_slot_gets_every_free_robot():
+    only_defense = _zone_split_picker(_game(0.0, 0.2, 0.8), FREE, None, frozenset({"defense"}))
+    assert only_defense == {"defense": FREE}
+    only_attack = _zone_split_picker(_game(0.0, 0.2, 0.8), FREE, None, frozenset({"attack"}))
+    assert only_attack == {"attack": FREE}
+    assert _zone_split_picker(_game(0.0, 0.2, 0.8), FREE, None, frozenset()) == {}