The Kassam Stadium fixture was held up for more than 15 minutes following the matter which saw a member of the U’s staff pick up a head injury in the tunnel area.
Pompey manager Danny Cowley told The News the incident happened while he and his players were in the away dressing room.
He also denied any of his squad were involved, despite the bad-tempered match itself seeing 11 yellow cards and one red handed out by referee Samuel Barrott.
The sending off happened 16 minutes into the game, with Pompey midfielder Joe Morrell dismissed for his challenge on Cameron Brannagan.
Yet, joining Cowley in keeping everyone in suspense as to what actually happened, opposite number Robinson said there was no hostility to the incident.
Although, the use of the term ‘tremendous’ in his explanation does little to dampen suspicion.
When asked by the Oxford Mail was happened, Robinson simply said: ‘Someone fell and just banged their head.
‘It was nothing, there was no tremendous malice in that.’
The second half resumed shortly after 4.25pm – after Barrott called time on the first period at 3.54pm.
And the drama didn’t end there, with the U’s coming back from 2-1 down with 10 minutes to go to record a 3-2 win thanks to late goals from Brannagan (82 minutes) and substitute Nathan Holland (90+6) as 10 minutes of injury-time were added on at the end.