Generations of British shoolboys were taught that, as an
effective sportsman, you will always have a highly developed sense
of competition; as a good sportsman, you will never let
competitiveness debase your conduct.
Generations of British schoolchildren have been taught that - in sport, as in life - it's not all about winning the game, it's about playing well. This means being magnanimous in victory, and gracious in defeat. Sportsmanship is no more than good manners: congratulating your opponents on effective play, accepting the decisions of the referee/umpire with good grace - absolutely no whining, arguing, sulking or triumphal strutting.
Increasingly, however, this behaviour is becoming the preserve of professional sportsmen. Gamesmanship can be defined as the art of winning unfairly at sport without actually cheating. If a player profits from an unfair advantage, or covers up an unjust act, or intimidates his opponent/s by words or body language he is guilty of gamesmanship, which is the antithesis of good sportsmanship.
Unfortunately, histrionic questioning of line calls, hectoring and haranguing referees/umpires and taunting and goading opponents permeate all levels of professional sport, from tennis to football. It is scarcely surprising, therefore, that amateurs are aping the less attractive attitudes of the professionals, and bending the rules in order to win.
Any tendency to employ these tactics should be eradicated. Good manners in sport are paramount, as in other aspects of life. Even if this means you lose again and again, at least you will be doing it gracefully.