Yep, allowed a fourth sub in case of suspected concussion. This then allows the other team an extra sub too to ensure fairness.
Preston keeper went off using a concussion sub, so they were still allowed three standard ones. In that circumstance they also allow the other team four subs, as Matt says above.
Yep I was there with brother in law. Early conclusion to Preston keeper, he did play on but then sank to his knees. So he was replaced by a concussion sub which gave Hull an extra sub. Not impressed with either side but Hull have a very good left winger lad called Keane Lewis-Potter. Murdered Preston. Keep him quiet and nowt to worry abart. Moncur and Wilks played for Hull (Moncur actually put a shift in). Potts and Lyndsay played for Preston, Potts came on 2nd half. Can see Preston struggling this year.