Parents have been banned from attending school sports days in more than 40 schools across south-west London
Adults have been seen "cutting across finish lines" to impede youngsters and shouting abuse towards officials and other children.
The Merton School Sports Partnership (MSSP) runs sporting activities in the area and informed parents that they would not be welcome to attend.
The MSSP sent a letter to parents in the borough, saying that some of the "officials" receiving abuse were young students helping out at the events.
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Parents had been told not to shout "specific orders" such as "shoot", "pass" or "go faster".
The newly-imposed ban is believed to cover a series of events, such as sports days, football and hockey tournaments and gymnastics competitions.
Some parents had also been found to share photos and videos on social media without parental consent.
The MSSP wrote a lengthy statement to parents about "respect".
Fights previously broke out between parents at an under-10s football match in Kent
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It wrote: "All children have the right to be able to take part in PE and sport without abuse, in a nurturing, growth mindset environment where they feel confident to make their own decisions and learn from their own 'marvellous mistakes'.
"Participants and officials should never be told by spectators and others, what to do and when to do it during their performance or game.
"Spectators can enjoy watching their friends and family taking part, and can make the event much more exciting with positive and encouraging generic support.
"Spectators should not call out specific orders or advice ('shoot', 'pass, 'go faster'), whilst the children are playing their game."
The MSSP concluded: "Nor should they shout anything unconstructive ('you're too slow'), derogatory/abusive comments or actively show and gesture their disappointment when a 'marvellous mistake' has been made by a player or official."
Any "concerning behaviour" will be reported by the MSSP as part of its "safeguarding protocol".
Wimbledon MP Paul Kohler said it was "deeply disappointing [that] the behaviour of a minority of parents has led to this outcome, which penalises the vast majority who have always behaved responsibly and supportively".
He noted: "Whilst I understand how disappointed those parents will be, I know they, like me, would not want any child, teacher, or volunteer to ever feel unsafe or threatened at what should be an enjoyable family-friendly event.
The MSSP said: 'Participants and officials should never be told by spectators and others, what to do and when to do it during their performance or game'
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"The focus must always be on creating a positive environment for young people to enjoy sport and develop teamwork and confidence.
"I hope this is a temporary measure to provide the space needed to reset expectations around respect and sportsmanship.
"With co-operation between the Merton School Sport Partnership, schools and parents, I am confident we can find a solution that addresses unacceptable conduct while allowing families to share in their children's sporting achievements."
Parents said they understood the decision, having witnessed "uber competitive adults" and "hideous behaviour" at sporting events.
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