Is "a group" singular or plural?

I was wondering what number the verb 'to snowboard' should take in the following sentence:

A group of men, led by Olympic athlete John Rider, snowboard(s) down the gently sloping hills.

Because 'a group snowboards', but 'they snowboard'. The second one sounds better to me.

But can anyone explain me the difference, and which one is right or wrong?

Solution 1:

If we are thinking about the group as a single entity, then we use snowboards. This would be the most common way to conceptualize your example sentence.

However, if we are thinking of members of the group individually, then British English users often use a singular verb with a collective noun. This is most apparent when BrEng users talk about companies as the individuals comprising them: BP have begun new drilling operations in Nigeria.

The crowd run off in every direction.

So, conceiveably: The group snowboard down the hill. (Conceptualized as, Each man at his own speed and in his own style). I don't know how often this is done with group, but it cannot fairly be called incorrect.

American English users more often make another type of change in order to preserve agreement in number between collective noun as singular, and verb--e.g., The members of the crowd run....

http://en.m.wikipedia.org/wiki/Comparison_of_American_and_British_English#Formal_and_notional_agreement