American sprinter Sha’Carri Richardson has issued a heartfelt apology to her boyfriend, fellow US runner Christian Coleman, after allegedly assaulting him at a US airport.

READ: Sha’Carri Richardson charged with domestic violence offence – reports

“I apologise to Christian. He came into my life and gave me more than a relationship but a greater understanding of unconditional love from what I’ve experienced in my past,” Richardson wrote in a post to her Instagram stories.

She said due to her “past trauma and pain”, she was “blind” and “blocked off” to receiving and expressing love.

“I love him and to him I can’t apologise enough,” Richardson wrote. “My [apology] should be just as loud as my actions, honestly louder.

“To Christian, I love you and I am sorry,” she concluded.

Richardson spent a night in jail late July after being detained, with a police report later stating she was caught on video repeatedly shoving Coleman forcefully.

Coleman sprang to the defence of Richardson in an interview last week, saying he believed she should not have been detained following the incident at Seattle-Tacoma Airport.

READ: Coleman defends ‘great person’ Richardson after assault controversy

“For me personally, I feel like it was a sucky situation all round,” Coleman said when asked about the incident by AFP. “I don’t feel like she should have been arrested.

“I mean people have discussions and emotions and stuff like that. She has things that she needs to work on for herself of course. So do I, so do you, so does everybody.

“But I’m the type of guy who’s in the business of extending grace, and mercy and love.”