A 26-year-old Derry man who cannot be named for legal reasons has pleaded guilty to child cruelty against his son, who was then aged two months.
Derry Crown Court heard that the man swung the baby back and forth by the left leg over a five minute period on October 26 2009 at his home.
A prosecution barrister said that immediately before the incident the baby had been crying and that immediately after the incident the baby squealed as if in pain and then went back to sleep in his cot.
The court heard that the baby's mother tried to intervene but her partner pulled the baby away and then when she tried to phone the police the defendant took the phone from her.
The matter was brought to the attention of the police in February 2010.
Judge Piers Grant was also told that a probation service report stated that the defendant did not present a risk of serious harm, and that there were no lasting effects arising from the incident.
Defence barrister, Martin Rodgers, said the defendant was a person of limited cognitive ability, and that there was no history of domestic violence prior to this incident.
He described the incident as 'a moment of madness' on the part of his client.
Judge Piers Grant said he accepted that it was a lower level case of child cruelty, and that it was an isolated incident.
He released the defendant on continuing bail until Monday when a date for his sentencing will be fixed.