Wainwright told the court that Corner was in “an unfamiliar place, an unfamiliar scenario, alarms going off, with a liquid toxic smell to the air”.
“Imagine how Mr Corner would have been feeling,” Wainwright said.
“Then you add in Leona Kamio’s screams [as she was being arrested],” he added.
Jurors heard Corner “genuinely thought” that Kamio or Rogers was being seriously injured when he brought the sledgehammer down on to Sgt Evans.
Sgt Evans previously told the trial she thought her spine was “shattered” when she was hit on her lower back while on her knees arresting a female activist.
The court previously heard she suffered a fractured spine and bruising as a result of the incident and was unable to return to work for three months.
Prosecutors said Corner struck Sgt Evans twice, but the officer told the court she only remembers being struck once.
“There was no sign that he was intending to continue,” Wainwright said.