Complex sentence: The coach was not entirely incorrect as Kosar's performance had diminished in recent years, but many the Browns fans saw this rejection as an insult, and some came to the next home game in Kosar masks.
Split into simpler sentences: The coach was not entirely incorrect-Kosar's performance had diminished in recent years. But the release of the popular player set off a wave of anger among Browns fans, some of whom came to the next home game in Kosar masks.