Which sentence contains a nonessential adjective clause?
The coach explained the rules that the officials revised in 2010.
The coach who is an expert in the sport explained the revised rules to us.
After explaining the rules to us, the coach released us to the field.
The officials revised the rules, which the coach explained to us before practice.

Question

Which sentence contains a nonessential adjective clause? 
 The coach explained the rules that the officials revised in 2010.
 The coach who is an expert in the sport explained the revised rules to us.
 After explaining the rules to us, the coach released us to the field. 
The officials revised the rules, which the coach explained to us before practice.

confusionist · Answer

The second one. Also, it's missing commas.