a fanatic ... crowd/crowds

[Tan Elaine]

Manager Alex Ferguson's 70th birthday was made one to forget after his side was upset 2-3 by the basement club Blackburn.

The host United, supported by a fanatic 75,146 crowds at Old Trafford, failed to impress due to their slack defending in the area, suffering a 0-2 blow after 51 minutes from a brace-scoring Ayegbeni Yakubu.

Why is 'crowds' used when 'a' precedes it?

Thanks.

[billmcd]

Manager Alex Ferguson's 70th birthday was made one to forget after his side was upset 2-3 by the basement club Blackburn.

The host United, supported by a fanatic 75,146 crowds at Old Trafford, failed to impress due to their slack defending in the area, suffering a 0-2 blow after 51 minutes from a brace-scoring Ayegbeni Yakubu.

Why is 'crowds' used when 'a' precedes it?

Thanks.

"A" is OK, but it should be "crowd".