What Was The Punisher Doing During The Defenders?

The lead character of The Punisher, Frank Castle, was absent from Marvel and Netflix’s The Defenders, and now we know where he was while the NYC heroes were teaming up.
Since Daredevil’s other allies joined the fight in The Defenders, fans found it curious that Castle wasn't called on in the series.
Of course, now that The Punisher season 1 has premiered, we know what Frank was up to while The Defenders were saving New York City.