The match day stewards are mostly volunteers whose function is to assist in the safe running of the stadium, things like manning entrance and exit gates, supervising stairwells, guarding access to non public parts of the stadium and reporting any problems to the stadium control room. They're not trained or equipped for riot control that's a police responsibility.
The stadium license issued by the local authority probably specifies a minimum number of staff to be present if the stadium is open to the public and I would think yesterdays match would qualify for that.
