The rules of tennis can be found here:

International Tennis Federation: https://www.itftennis.com/officiating/rulebooks/rules-of-tennis.aspx

Note: rules can vary between competitions.
This document describes the V3 tennis match state contract.

Match Summary Message

The summary message summarises the major match events into a single, easily digested message.

{
"Source":Betgenius,
"BetgeniusFixtureId":3415011,
"SourceFixtureId":null,
"BookmakerId":6002,
"CompetitorA":{},
"CompetitorB":{},
"IsReliable":true,
"IsScoreConfirmed":True,
"StateOfPlay":"BetweenPoints",
"Server":"CompetitorA",
"Match":{},
"StartedAt":"2015-10-01T15:15:40.951Z",
"FinishedAt":null,
"MessageTimestampUtc":"2015-10-01T15:15:44.955Z"
}

Element	Type	Description
Source	String	The source of the data, typically the name of the company analysing the match
BetgeniusFixtureId	Integer	An immutable identifier for the fixture
SourceFixtureId	String	The fixture ID used by the data source if data source is not Betgenius
BookmakerId	Integer	An immutable identifier for the customer
CompetitorA	CompetitorDetails	An object that describes Competitor A
CompetitorB	CompetitorDetails	An object that describes Competitor B
IsReliable	Boolean	True if the data values are reliable, False otherwise
IsScoreConfirmed	Boolean	True if this score has been confirmed, False otherwise
StateOfPlay	MatchStatus	An enum describing the current state of play. Values: NotStarted WalkoverCompetitorOne (CompetitorOne wins) WalkoverCompetitorTwo (CompetitorTwo wins) OnCourt WarmingUp BetweenPoints PointInProgress Challenge PlaySuspended ShortDelay MedicalTimeoutCompetitorOne MedicalTimeoutCompetitorTwo WinnerCompetitorOneByRetirementOrDefault WinnerCompetitorTwoByRetirementOrDefault WinnerCompetitorOne WinnerCompetitorTwo
Server	CompetitorIdentifier	An object that indicates which competitor is serving
Match	Match	An object that describes the match score
StartedAt	DateTime, optional	The UTC time that the fixture started, if complete; null otherwise
FinishedAt	DateTime, optional	The UTC time that the fixture ended, if complete; null otherwise
MessageTimestampUtc	DateTime	The UTC time that the message is sent

CompetitorDetails

Describes a player in a tennis match.

{
"Id":"6546872",
"Name":"Andy Murray"
}

Element	Type	Description
Id	String	An immutable ID for the player
Name	String	The name of the player

Match

Describes the current score in a tennis match.

{
"MatchScore":{},
"IsMatchComplete":false,
"IsDataComplete":true,
"Sets":[],
"Statistics":{}
}

Element	Type	Description
MatchScore	Score	An object that describes the score in sets, games and points
IsMatchComplete	Boolean	True if the match is complete, false otherwise
IsDataComplete	Boolean	True if the data is complete, false otherwise
Sets	Set	An array of set objects
Statistics	CompetitorStatistics	An object holding statistics for each competitor

Set

Describes the score in a set of a tennis match.

{
"SetNumber":1,
"SetScore":{},
"IsSetComplete":true,
"IsDataComplete":true,
"SetType":Advantage,
"Games":[],
"Statistics":{},
"TieBreakStartsAt":1
}

Element	Type	Description
SetNumber	Short	The number of the set within the match
SetScore	Score	The set score in games
IsSetComplete	Boolean	True if the set is complete, false otherwise
IsDataComplete	Boolean	True if the data is complete, false otherwise
SetType	SetType	An enum indicating the rules that will determine how the set winner will be decided if the score reaches 6-6. Values: Advantage Tiebreak MatchTiebreak
Games	Game	An array of game objects detailing the outcome of individual games
Statistics	CompetitorStatistics	An object holding statistics for each competitor
TieBreakStartsAt	Integer	Null or an integer, defines the number of tied games (6-6,10-10,12-12) required for the tiebreak to start in this specific set. Example, if the tie break starts at 6-6 the value is 6 If tie break is not used, the value is set to null

CompetitorStatistics

Contains statistics about a players performance within the set or match.

{
"Competitor":{},
"FirstServeAces":2,
"FirstServePointsWonByServer":4,
"FirstServePointsWonByReceiver":4,
"SecondServeAces":0,
"SecondServeFaults":0,
"SecondServePointsWonByServer":0,
"SecondServePointsWonByReceiver":0,
"BreakPointsFaced":0,
"BreakPointsLost":0
}

Element	Type	Description
Competitor	CompetitorIdentifier	An array describing the competitor to whom these statistics apply
FirstServeAces	Short	The number of aces awarded to the player from their first serve
FirstServePointsWonByServer	Short	The number of points won by the server on their first serve
FirstServerPointsWonByReceiver	Short	The number of points won by the receiver from the server's first serve
SecondServeAces	Score	The number of aces awarded to the player from their second serves
SecondServeFaults	Short	The number of double faults committed by the player
SecondServePointsWonByServer	Short	The number of points won by the server on their second server
SecondServePointsWonByReceiver	Short	The number of points won by the receiver on the server's second server
BreakPointsFaced	Short	The number of break points faced by the competitor
BreakPointsLost	Short	The number of break points lost by the competitor

Game

Describes the score in a game of a tennis match.

{
"GameNumber":1,
"GameScore":{},
"IsGameComplete":true,
"IsDataComplete":true,
"GameType":Standard,
"Points":[]
}

Element	Type	Description
GameNumber	Short	The number of the game within the set
GameScore	Score	The game score in points and in standard tennis format
IsGameComplete	Boolean	True if the game is complete, false otherwise
IsDataComplete	Boolean	True if the data is complete, false otherwise
GameType	GameType	An enum indicating how the winner of the game will be decided if the score reaches 40-40. Values: Standard NoAd Tiebreak MatchTiebreak
Points	Point	An array of point objects detailing the outcome of individual points

GameScore

Describes the score in a game of a tennis match.

{
"DisplayCompetitorOneScore":"30",
"DisplayCompetitorTwoScore":"40",
"CompetitorOneScore":2,
"CompetitorTwoScore":3,
}

Element	Type	Description
DisplayCompetitorOneScore	String	Competitor One's score in standard tennis nomenclature. Values for normal game: 0 15 30 40 A Game In a tiebreak game, score will be presented as an integer.
DisplayCompetitorTwoScore	String	Competitor Two's score in standard tennis nomenclature. Values for normal game: 0 15 30 40 A Game In a tiebreak game, score will be presented as an integer.
CompetitorOneScore	Short	A count of points scored by Competitor One
CompetitorTwoScre	Short	A count of points scored by Competitor Two

Match Details Message

Tennis match details messages provide the same kind of data as summaries do, however a full timeline of the event is kept available within any given message.

{
"Source":Betgenius,
"BetgeniusFixtureId":3415011,
"SourceFixtureId":null,
"BookmakerId":6002,
"CompetitorA":{},
"CompetitorB":{},
"IsReliable":true,
"IsScoreConfirmed":True,
"StateOfPlay":"BetweenPoints",
"Server":"CompetitorA",
"Match":{},
"MessageTimestampUtc":"2015-10-01T15:15:44.955Z"
}

Element	Type	Description
Source	String	The source of the data, typically the name of the company analysing the match
BetgeniusFixtureId	Integer	An immutable identifier for the fixture
SourceFixtureId	String	The fixture ID used by the data source if data source is not Betgenius
BookmakerId	Integer	An immutable identifier for the customer
CompetitorA	CompetitorDetails	An object that describes Competitor A
CompetitorB	CompetitorDetails	An object that describes Competitor B
IsReliable	Boolean	True if the data values are reliable, False otherwise
IsScoreConfirmed	Boolean	True if this score has been confirmed, False otherwise
StateOfPlay	MatchStatus	An enum describing the current state of play. Values: NotStarted WalkoverCompetitorOne (CompetitorOne wins) WalkoverCompetitorTwo (CompetitorTwo wins) OnCourt WarmingUp BetweenPoints PointInProgress Challenge PlaySuspended ShortDelay MedicalTimeoutCompetitorOne MedicalTimeoutCompetitorTwo WinnerCompetitorOneByRetirementOrDefault WinnerCompetitorTwoByRetirementOrDefault WinnerCompetitorOne WinnerCompetitorTwo
Server	CompetitorIdentifier	An object that indicates which competitor is serving
Match	Match	An object that describes the match score
MessageTimestampUtc	DateTime	The UTC time that the message is sent

Points

Describes a point in a game of a tennis match.

{
"PointNumber":1,
"Server":{},
"IsInSequence":true,
"IsDataComplete":true,
"Actions":[]
}

Element	Type	Description
PointNumber	Short	The number of the point within the game
Server	CompetitorIdentifer	An object that indicates which competitor is serving
IsInSequence	Boolean	True if Point is in sequence, false otherwise
IsDataComplete	Boolean	True if the data is complete, false otherwise
Actions	PointAction	A collection of point actions describing the history of the point

PointAction

Describes a point in a game of a tennis match.

{
"ActionType":PointStarted,
"TimestampUtc":"2015-10-01T15:15:44.9551641Z"
}

Element	Type	Description
ActionType	PointActionType	The type of point action. Values PointStarted Let Fault Ace ServerWon ReceiverWon ChallengeServer ChallengeReceiver ChallengeFailed ChallengeSuccessful
TimestampUtc	Datetime	The time in UTC at which the action was recorded by the Umpire