Where a defendant has filed an answer without pleading an affirmative defense, may the defendant nonetheless assert that affirmative defense as the basis for a summary judgment motion, without amending or seeking to amend its answer to plead that affirmative defense, and may a defendant do so even if an amendment adding that affirmative defense would be barred by Rule 16(b)(4)?

Whether a defendant may assert an affirmative defense in a summary judgment motion without previously pleading it in an answer, despite Rule 8(c)(1) and potential Rule 16(b)(4) limitations