Complex sentence: The arena has a seating capacity of 12,000 or 13,000 in a standing performance.Its official opening was on September 30,2013 with the staging of a concert by Rod Stewart.
Split into simpler sentences: The arena has a seating capacity of 12,000 or 13,000 in a standing performance. It had its official opening on September 30,2013 with the staging of a concert by Rod Stewart.