No, if the critic lacks either the knowledge or the temperament to be a good critic, then the reasonable response is either, "You're fired" (if you are running the media outlet), or "I will ignore you" (if you're a fan). The critic's personal skills in the field remain irrelevant.
Now you are trying to change the argument by asserting that a critic can't have developed the necessary understanding of a field without having participated in it as a performer at a very high level. Although that claim would require a field-by-field analysis to be comprehensively refuted, I think it's safe to declare that it's generally wrong. There have been lots of excellent critics and experts in many fields, including tennis, who have never been professional performers in those fields. You are confusing the type of learning necessary to understand tennis with the type of learning necessary to play tennis. It's true that you can't acquire actual tennis skills from reading books and watching matches on TV, but that doesn't mean you can't develop a deep awareness of what the players are doing.
The reason that televised sports originally introduced former athletes as "color commentators" alongside the play-by-play announcers was not that the broadcast professionals didn't know what they were talking about. The belief was that fans would enjoy the different -- not better or wiser -- behind-the-scenes perspective that the ex-jocks could provide. Apparently some fans now have arrived at the conclusion that only former athletes have the right or the ability to comment negatively on the work of current athletes, but that's just not correct.
What I said was "The most thorough understanding of a field is given by the capacity to perform in it." I never made a comment about critics being
incapable of having developed the necessary understanding of a field without having
professionally participated. What I did say was that those who have actually participated in the field and acquired a
degree of excellence in it have
greater understanding than that of the critic.
Usually what a critic brings is eloquence and an ability to make one's observations salient. What a professional, especially a top professional, brings is the highest degree of understanding proven through experience. Bud Collins or even Brad Gilbert may be great communicators and eloquently describe the qualities needed to win a grand slam final, but Pete Sampras, whatever his communicative abilities are, inherently understands these qualities to a far greater degree because he embodies them. He won 14 times. Neither Gilbert nor Collins would dispute this.
If you combine an excellent former professional with great communicative skills you have the zenith of commentary. I think Andre Agassi offered one of the best commentaries in recent years during the Federer - Roddick US Open match of 2007. He described the unique challenges Federer poses, some of the ways Roddick could improve his backhand, and gave perspective on the dynamics of competitive matchplay. A non-professional, and even a non-all time great would not have been able to offer such illumination. Agassi's unique experience having played Federer, having unique hand eye coordination and ball striking abilities on both wings, and his breadth of experience winning high level grand slam matches gave his commentary extra weight.
This is a side point, but what I particularly enjoyed about Agassi's commentary was that he offered incredibly insightful, salient points without a hint or taste of criticism. For example, when talking about Roddick's backhand, he didn't deride it as weak, but instead offered suggestions on improvement, talking about the common strands in all great two handed backhands. Or when discussing Fed, he didn't gush, he offered very clear reasons as to why he was such a unique talent. The discussion about how Federer times the ball was eye opening. All in all, great great commentary.
