In the sentence "Pat, who won the prize, deserves our congratulations," what can be said about the clause "who won the prize"?

The clause "who won the prize" is a non-restrictive relative clause, which means it provides additional, non-essential information about the noun it modifies, in this case, "Pat." Since the main point of the sentence is that Pat deserves congratulations, the clause adds interesting context without affecting the overall meaning. If you removed the clause, the core message—that Pat deserves our congratulations—remains clear and intact.

In non-restrictive clauses, commas are used to set off the information that is not critical to the meaning of the sentence. This indicates that the details provided in the clause serve to enhance the reader's understanding but are not required for identification or comprehension of the primary subject.