He has also denied a charge of assaulting Ms Wickliffe with intent to injure, one of assaulting her and one charge of attempting to pervert the cause of justice by threatening her.
In his closing address yesterday, Tauranga Crown solicitor Greg Hollister-Jones described Boynton as a man with a "short and violent temper" that escalated to violence over seemingly minor issues.
Mr Hollister-Jones said that on April 28 Boynton was stressed and angry as Ms Wickliffe had left him and the teething baby days earlier. He said at 6pm that day Boynton went into his crying but otherwise healthy son's bedroom and came back 20-30 seconds later holding the seriously concussed baby.
Boynton had a history of "snapping" when his baby cried.
Mr Hollister-Jones said a doctor had testified the concussion could have been caused by shaking, slamming him on to a surface or a combination of both. The haemorrhaging in the baby's eyes was said to be more serious than you would see from a high speed motor accident.
Boynton's lawyer Tony Rickard-Simms said his client had accepted his shortcomings and was not proud of slapping and pushing Ms Wickliffe. However, he denied allegations he intended to injure her or that he had harmed his baby.
"He loves his children, all of them. He is very proud of them," said Mr Rickard-Simms.
When Boynton heard the baby cry he recognised something was not right, so he brought the baby straight back out and asked friends for help. An ambulance was then called.
"We say he in fact saved his baby's life that night."