Levi-Blu Cassin died from abdominal injuries in 2013
A man accused of murdering his 22-month-old son in Birmingham had previously punched his other son in the stomach, a court heard.
Mark Piper is jointly charged with murdering Levi Blu.
Levi died in 2013 of internal bleeding. His mother Danielle Cassin is also accused of murder.
A woman told a jury at Birmingham Crown Court she saw Mr Piper being violent with his other child, who was five at the time, in 2012.
'Poked in face'
The incident happened in the living room of Mr Piper's Chelmsley Wood home after he banned the youngster from playing on a games console, she said.
The witness said Mr Piper swore at his son and dragged him out the room before poking and prodding him in the face by the stairs.
"He (the child) was crying," said the woman, who met 31-year-old Mr Piper through a mutual friend.
"He punched him in his stomach at the same time on the stairs. It was hard, enough to hurt him.
"I have never seen anyone hitting a kid like that. It was rough. It was how you would hit your friends messing about. The little boy was crying. He was really upset."
But Paul Lewis QC, defending Mr Piper, wanted to know why the punch was not mentioned in her original police statement.
"I was lying (to the police)," she said.
"I didn't want to seem like a grass."
'Loves his kids'
Mr Lewis questioned how she could be sure about the words Mr Piper had used when she made her police statement months after the incident.
He highlighted a message sent by the witness about Piper which said: "He loves all his kids and looks after them well. I just don't understand all this."
Levi was found at the flat his parents shared in Nightingale Avenue, Chelmsley Wood, on 20 February 2013.
Both Ms Cassin, 27, of Frensham Close, Chelmsley Wood, and Mr Piper, of no fixed abode, deny murder.
They also deny causing or allowing the death of Levi and causing him suffering.
The trial continues.