Answer:
The prejudice shown is making a sexist remark against the female gender.
The line "Women don't know the offside rule" shows how sexist the comment is.
Explanation:
A sexist remark is when a person of one gender says something discriminatory about a person of another gender. This means that talking bad about the other based on her gender is known or taken as a sexist comment or discrimination based on one's gender.
In the given scenario of the sports presenters, their comment about Sian Massey's 'incapability' to be a referee, based on her being a woman is a sexist remark. They are making the claim that Sian was not worthy to be a referee for the game because of her gender and that women don't know anything about <em>"offside rule"</em> which is discriminatory in nature.
This claim can be supported by the very comment <em>"Can you believe that? A female linesman. Women don't know the offside rule."</em>
