According to Official Guinness Records,
The loudest crowd roar at a sports stadium is 142.2 dbA and was achieved by fans of the Kansas City Chiefs (USA), at Arrowhead Stadium in Kansas City, Missouri, USA, on 29 September 2014.The roar was recorded with 8 seconds remaining in the first quarter. The Chiefs defeated the New England Patriots 41-14.Read more: Kansas City Chiefs fans reclaim record for loudest crowd roar at sports stadium
For a complete list of 2014 records, please visit 2014 Guinness Records in United States.