Its not a case of practicing, it because people are charged £ into the event. Even if it was second halves , the crowd will have been charged to enter the original meeting
My local football league club once had a player on trial from a non EU country and wanted to see him action. Normally it was a couple of quid to get into the reserve games . They wanted to see him in a game and to get around the work permit issue, just opened the doors for free and therefore at the time were not contravening any laws .
This was a while since and i'm sure this loophole may have been changed.