Complex sentence: One exception to the rule was be the Bavarian club FC Bayern Alzenau, traditionally playing in Hesse's league system, which was be grouped in the new Regionalliga Südwest, upon their own request, rather than in the Regionalliga Bayern.
Split into simpler sentences: One exception to the rule was the Bavarian club FC Bayern Alzenau, who had traditionally played in Hesse's league system. This club would participate in the new Regionalliga Südwest, at their own request, rather than in the Regionalliga Bayern.