It isn't the baseball player who is sinning, so his fellow baseball player doesn't need to comment on it. Talking about how the Mother is sinning certainly won't change the player's mind, nor his mother's, so why be rude about it? Just to satisfy some need to 'be a witness'? You can witness without saying a word, and sometimes that's the best way.
Again, Sean Casey is a Traditional Catholic. Traditional Catholicism teaches that silence in the face of the sin of another is itself a sin. That Valentine's mother and her pervert partner are sinning is beyond question. Valentine participates in their sin at the very least by consent and by praising their persistence in sin. Casey, according to his own purported belief system, would become an accessory to that sin by remaining silent while Valentine flaunts it.
Now, you and the ACLU can consider that "rude" or "forward" or "witnessing" or whatever you want, but you would be on the wrong side of almost 2000 years of Catholic Tradition. The consequences of that may be just dandy with you, but Mr. Casey has publicly expressed his belief in such a Tradition. My original post expressed curiosity as to what he may have said about Valentine's situation. I frankly couldn't care less what you would do, since you obviously don't share his beliefs. But thanks for sharing anyway.