Complex sentence: Robinson also refereed the match between Brock Lesnar and The Undertaker at SummerSlam 2015 where the match ended in controversy after Undertaker tapped out to Lesnar, but Robinson didn't see it but the timekeeper saw it and rang the bell.
Split into simpler sentences: Robinson also refereed the match between Brock Lesnar and The Undertaker at SummerSlam 2015 where the match ended in controversy after Undertaker tapped out to Lesnar. Even though Robinson didn't see Undertaker tapping, the timekeeper saw it and rang the bell.