Yes, it is B, it is a defining relative clause, notice that without the relative clause the sentence feels empty <em>Only the players are going to get sunburned today. </em>
Defining relative clauses use <em>who/that</em> for people, <em>which/that</em> for things and they are not delimited by commas.
<em>Only the people that/who arrived first can enter.</em>
<em>This the house that/which I used to live in.</em>
Non-defining clauses are just extra comments, optionally they can be removed about the previous noun/pronoun, they are separed by commas and <em>that</em> cannot be used.
<em>Mary,who wears glasses, lives next door.</em>
<em>This country, which was a super power in the past, is still facing amajor economic crisis.</em>
