Boeing say there isn't one, but essentially it's the upwind outboard engine in a crosswind.
With rudder already being used to counter the crosswind on the takeoff roll, failure of the upwind outboard engine leaves less than full rudder to use to counter the asymmetry from the engine failure.
There has been debate here with all the history and the FAA/ARB/JAR certification issues, but a failure of THAT engine during max crosswind is pretty low. A smarter user may post a link to the earlier debate.
G'day
