Cork city marathon

http://www.aaireland.ie/AA/AA-Roadwatch/Event-Guide/Sports-Events/Cork-City-Marathon.aspx

How big a disruption is this likely to cause for Pats fans?

I'd give a bit more time anyway. The course is here - goes right by the ground. Also, it's a relay - you can have a team of up to four - so there'll be people being transported back to the start/finish line all the time. The relay change points would be particularly busy; don't know where they are this year though. Given the kick-off time, maybe the handiest would be to get the train down and back and walk/bus it to the ground.