Children as young as eight are victims of mental and physical bullying on the school playing field, according to new research.
Two-thirds (66%) of 1,010 parents of children aged eight to 16 said they witnessed different forms of mental intimidation while watching their children play sport, the study by Marylebone Cricket Club (MCC) and the Chance to Shine campaign found.
Teasing (43%), swearing (40%), taunts (34%) and verbal threats (16%) were common tactics of the sports bullies.
More than two fifths of parents (42%) said their child lost confidence after being bullied on the playing field, and a fifth felt their child was reluctant to take part in sport as a result of the mind games.
In a separate survey of 1,250 children, aged eight to 16, more than two thirds (68%) said they, too, saw verbal abuse during school matches and more than half (51%) admitted to being a victim of teasing, taunts and threats on the field.
The majority (55%) also witnessed physical violence, with a quarter of children seeing a team mate deliberately tripped, kicked or pushed over.
To help teach young people how to play matches in a competitive but sporting manner, MCC and grass roots sport campaign Chance to Shine are delivering a nationwide scheme to encourage "fair play" in schools.
Chance to Shine coaches are delivering assemblies and lessons in good sportsmanship to around half a million children in 4,000 state schools, as part of the MCC Spirit of Cricket scheme.
John Stephenson, head of cricket at MCC, said: "The results from the survey highlight an alarming trend in school sport, which needs to be proactively addressed. MCC's ongoing partnership with Chance to Shine provides the perfect vehicle to do this, as children get the opportunity to learn about the MCC Spirit of Cricket principles of playing hard, but fair."
Wasim Khan, chief executive of Chance to Shine, added: "It is worrying to hear that this kind of psychological warfare is being waged on our school playing fields. We are teaching children from a young age to play competitively, but to respect the opposition as well as their team mates. We need to stamp out this bullying in school sport."