Subs with DP/FLEX

[Duke]

Let me take a crack at this.
What confuses me is the statement:

"A sub is entered for DP/FLEX as the team is taking the field. FLEX player remains on the bench."

Sub needs to enter either for the DP OR the FLEX. I'll assume that by FLEX remaining on the bench that this sub is coming in for the FLEX. If this is the case then, no, the sub cannot be designated as the DP playing defense for the FLEX because the sub IS the FLEX.

Probably missing something here in the interp of you post.