Is there a way to disable a field on edit if it has data in it using script?

Example:

I have a service ticket for my field techs. One guy will add a record, then another will edit and add more data. I'm looking for a way to prevent the second guy from deleting data from the first guy. Each guy opens and edits the record multiple times so just can't disable on edit...only if data is there is what I need.

Thanks