Reading the call sheet
Loading the next OpenPlay view.
defense / zone coverage
Three deep defenders divide the field while a safety rotates down to handle the strong curl-flat and run support.
Animated assignment view
The strong safety holds split-safety depth before rotating into the curl-flat at the snap.
Ball at the line
How it works
Both corners take outside thirds, the free safety controls the middle third, and four underneath defenders distribute short zones. The sky rotation uses a safety as the strong-side force player.
Balance deep-ball protection, underneath vision, and an extra safety near the run fit from a flexible shell.
Three defenders guard the deep field, and a safety moves closer to the line to help against short passes and runs.
The curl-flat defenders must carry number two vertically long enough to protect the seams without surrendering immediate throws outside.
Call structure
The strong safety begins at split-field depth and rotates after the snap while the free safety moves to the deep middle.
{
"schema": "openplay-football",
"schemaVersion": "0.1",
"id": "cover-3-sky",
"slug": "cover-3-sky",
"name": "Cover 3 Sky",
"side": "defense",
"category": "zone-coverage",
"personnel": {
"id": "nickel-personnel",
"name": "Nickel",
"grouping": "4 DL, 2 LB, 3 CB, 2 S",
"positionCounts": {
"DL": 4,
"LB": 2,
"CB": 3,
"S": 2
}
},
"formation": {
"id": "under-front",
"name": "Under Front",
"family": "four-down",
"strength": "left",
"description": "The line shades away from strength while a safety rotates down as the strong curl-flat defender."
},
"situationTags": [
"single-high",
"zone-coverage",
"early-down"
],
"players": [
{
"id": "le",
"position": "DE",
"label": "E",
"initialCoordinate": {
"x": 20,
"y": 1
},
"alignment": "Left edge",
"side": "defense",
"ratingRole": "passRush"
},
{
"id": "dt",
"position": "DT",
"label": "T",
"initialCoordinate": {
"x": 25,
"y": 1
},
"alignment": "Three technique",
"side": "defense",
"ratingRole": "passRush"
},
{
"id": "nt",
"position": "DT",
"label": "N",
"initialCoordinate": {
"x": 28,
"y": 1
},
"alignment": "Shade",
"side": "defense",
"ratingRole": "runDefense"
},
{
"id": "re",
"position": "DE",
"label": "E",
"initialCoordinate": {
"x": 34,
"y": 1
},
"alignment": "Right edge",
"side": "defense",
"ratingRole": "passRush"
},
{
"id": "will",
"position": "LB",
"label": "W",
"initialCoordinate": {
"x": 22,
"y": 6
},
"alignment": "Weak hook",
"side": "defense",
"ratingRole": "zoneCoverage"
},
{
"id": "mike",
"position": "LB",
"label": "M",
"initialCoordinate": {
"x": 29,
"y": 6
},
"alignment": "Middle hook",
"side": "defense",
"ratingRole": "zoneCoverage"
},
{
"id": "lcb",
"position": "CB",
"label": "C",
"initialCoordinate": {
"x": 6,
"y": 6
},
"alignment": "Left third",
"side": "defense",
"ratingRole": "zoneCoverage"
},
{
"id": "nickel",
"position": "CB",
"label": "N",
"initialCoordinate": {
"x": 16,
"y": 5
},
"alignment": "Weak curl-flat",
"side": "defense",
"ratingRole": "zoneCoverage"
},
{
"id": "rcb",
"position": "CB",
"label": "C",
"initialCoordinate": {
"x": 48,
"y": 6
},
"alignment": "Right third",
"side": "defense",
"ratingRole": "zoneCoverage"
},
{
"id": "strong",
"position": "S",
"label": "S",
"initialCoordinate": {
"x": 37,
"y": 10
},
"alignment": "Rotation safety",
"side": "defense",
"ratingRole": "tackling"
},
{
"id": "free",
"position": "S",
"label": "F",
"initialCoordinate": {
"x": 27,
"y": 16
},
"alignment": "Deep middle",
"side": "defense",
"ratingRole": "zoneCoverage"
}
],
"preSnap": {
"description": "The strong safety holds split-safety depth before rotating into the curl-flat at the snap.",
"shifts": []
},
"assignments": [
{
"id": "left-third",
"playerId": "lcb",
"type": "zone-coverage",
"zone": [
{
"x": 0,
"y": 8
},
{
"x": 18,
"y": 8
},
{
"x": 18,
"y": 35
},
{
"x": 0,
"y": 35
}
],
"responsibility": "Protect the left deep third and stay above outside verticals."
},
{
"id": "middle-third",
"playerId": "free",
"type": "zone-coverage",
"zone": [
{
"x": 16,
"y": 10
},
{
"x": 38,
"y": 10
},
{
"x": 38,
"y": 35
},
{
"x": 16,
"y": 35
}
],
"responsibility": "Stay on top of seams and posts in the deep middle."
},
{
"id": "right-third",
"playerId": "rcb",
"type": "zone-coverage",
"zone": [
{
"x": 36,
"y": 8
},
{
"x": 53,
"y": 8
},
{
"x": 53,
"y": 35
},
{
"x": 36,
"y": 35
}
],
"responsibility": "Protect the right deep third and stay above outside verticals."
},
{
"id": "sky-curl-flat",
"playerId": "strong",
"type": "zone-coverage",
"zone": [
{
"x": 36,
"y": 1
},
{
"x": 53,
"y": 1
},
{
"x": 53,
"y": 13
},
{
"x": 34,
"y": 13
}
],
"responsibility": "Rotate down to the strong curl-flat and force runs inside."
},
{
"id": "weak-curl-flat",
"playerId": "nickel",
"type": "zone-coverage",
"zone": [
{
"x": 0,
"y": 1
},
{
"x": 19,
"y": 1
},
{
"x": 19,
"y": 13
},
{
"x": 0,
"y": 13
}
],
"responsibility": "Carry the weak seam before expanding to the flat."
},
{
"id": "mike-hook",
"playerId": "mike",
"type": "zone-coverage",
"zone": [
{
"x": 18,
"y": 3
},
{
"x": 36,
"y": 3
},
{
"x": 36,
"y": 14
},
{
"x": 18,
"y": 14
}
],
"responsibility": "Close crossers and protect the middle hook."
},
{
"id": "left-rush",
"playerId": "le",
"type": "pass-rush",
"path": [
{
"type": "straight",
"to": {
"x": 23,
"y": -7
}
}
],
"technique": "Contain"
},
{
"id": "tackle-rush",
"playerId": "dt",
"type": "pass-rush",
"path": [
{
"type": "straight",
"to": {
"x": 26,
"y": -6
}
}
],
"technique": "Penetrate"
},
{
"id": "nose-rush",
"playerId": "nt",
"type": "pass-rush",
"path": [
{
"type": "straight",
"to": {
"x": 28,
"y": -6
}
}
],
"technique": "Pocket push"
},
{
"id": "right-rush",
"playerId": "re",
"type": "pass-rush",
"path": [
{
"type": "straight",
"to": {
"x": 31,
"y": -7
}
}
],
"technique": "Contain"
}
],
"timeline": [
{
"type": "pre-snap",
"atMs": 0
},
{
"type": "snap",
"atMs": 500
},
{
"type": "assignment-start",
"atMs": 550,
"playerId": "strong"
},
{
"type": "play-end",
"atMs": 4500
}
],
"narrative": {
"summary": "Three deep defenders divide the field while a safety rotates down to handle the strong curl-flat and run support.",
"fullExplanation": "Both corners take outside thirds, the free safety controls the middle third, and four underneath defenders distribute short zones. The sky rotation uses a safety as the strong-side force player.",
"strategicPurpose": "Balance deep-ball protection, underneath vision, and an extra safety near the run fit from a flexible shell.",
"idealSituations": [
"First down",
"Against balanced formations",
"When defending both run and pass"
],
"strengths": [
"Three-deep protection",
"Strong run support",
"Eyes on the quarterback"
],
"weaknesses": [
"Seams stress the free safety",
"Curl-flat defenders face high-low conflicts",
"Four verticals can isolate thirds"
],
"keyRead": "The rotating safety keys the end receiver while the middle safety opens toward the strongest vertical distribution.",
"watchFor": [
"The safety rotating down",
"Corners bailing into thirds",
"Hook defenders passing crossers"
],
"beginnerExplanation": "Three defenders guard the deep field, and a safety moves closer to the line to help against short passes and runs.",
"advancedNote": "The curl-flat defenders must carry number two vertically long enough to protect the seams without surrendering immediate throws outside."
},
"simulation": {
"difficulty": "intermediate",
"conceptTags": [
"zone-coverage",
"cover-three",
"single-high"
],
"baseSuccessRate": 0.6,
"yardRange": {
"min": -10,
"max": 45
},
"turnoverRisk": 0.04
},
"defensiveStructure": {
"front": "Under four-down front",
"personnel": "Nickel 4-2-5",
"coverage": "Cover 3 Sky",
"rushPlan": "Rush four with sound lane integrity while the strong safety supplies underneath support.",
"runFits": [
"Strong safety forces outside runs",
"Linebackers fit interior gaps",
"Weak nickel handles cutback support",
"Ends maintain contain"
],
"disguise": "The strong safety begins at split-field depth and rotates after the snap while the free safety moves to the deep middle.",
"strengths": [
"Balanced early-down structure",
"Three deep zones",
"Safety run support"
],
"weaknesses": [
"Seam routes",
"Curl-flat stretches",
"Flood concepts"
],
"idealSituations": [
"First down",
"Open field",
"Balanced offensive tendency"
],
"vulnerableConcepts": [
"four-verticals",
"curl-flat",
"play-action-cross"
]
}
}