If there are more winners for a wager than expected then the payouts for these wagers will be reduced due to the dead heat rule. This is most common in Golf wagering especially for wagers such as Top 10, Top 20..etc.
For example you make a $10 wager for a golfer to finish in the top 20 at +500. Once the tournament finishes four golfers are tied for 19th (including your golfer).
In this case all golfers positioned 1-18 will receive payouts as normal, however the four golfers at position 19 are level for two available winning places (19th and 20th).
Therefore your winnings can be calculated as follows:
Number of winning places available (2) divided by the number of players tied (4) = (0.5)
Your winnings will therefore be (0.5x) what your wager would have ordinarily won. Given a $10 wager at +500 would usually pay $60 total, in this case you would get $30 ($60 x 0.5).