When to Overrule?

[SamNVa]

One umpire should NEVER EVER overrule another umpire.

The second umpire can let the first umpire know if they have seen something that might affect the first umpire's call (e.g. the second umpire might see a ball rolling on the ground after a out call on a tag), but the call still remains with the first umpire.

It happens, on occasion the both umpire's will make a call on the same play. It isn't supposed to happen, but sometimes it does. In this case, the umpires should get together and parlay, but the ultimate call resides with the PU in this case.