You need to combine the RANK() function with a COUNTIF() function.
Rank deals with ties by skipping ranks. If 2 players tie for top score then there will be no rank value of 2 - instead there will be two 1's and then a 3.
The COUNTIF() checks for that.
See this link for a detailed description: http://www.cpearson.com/excel/Rank.aspx