It is possible to lock a field after the user has entered text into it and clicks or tabs out.
Use this as the Custom Keystroke script for the Company Name field:
if ( this.value !="" && event.willCommit != 0 )
this.getField("Text1").readonly = true;
Replace "Text1" with the Company Name field in your form.
I don't know if it is possible to limit the number of attempts to 2-3 before it becomes locked.
