There was a similar challenge recently in an early FA cup game between Eastleigh and Newport and the player , on a booking, was given a straight Red. I thought the Red was very harsh but an absolute stick on booking.
Duk was rightly booked then seconds later Sterling goes round him on the halfway line and Duk slips and as he’s falling he tap tackles Sterling’s ankle and stops / slows the break. Again an absolute stick on booking but Robertson went to blow for the foul but allowed advantage therefore he can’t give the second yellow.
Also recent Old Firm shame game and Alistair Johnstone , on a booking, does the same forearm challenge on Sima and nothing. No red card, no second yellow just Sima taken off with head knock / concussion!
It’s not one or two isolated incidents. It’s on a weekly basis.
It’s not exactly a secret that Celtic and Peter Lawwell in particular have an unhealthy hold on Scottish football and until that hold is broken this will continue!