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Certainly borderline, and basicallly because its connection to Arthurian legends, but more closely related to the Legend of The Fisher King, or the Wounded King, thus more likely predating Arthurian Myth.
Other connections to Arthur are the involvement with 'fallen' (stands for evil?) women which signals the king's downfall, though not necessarily directly, and not necessarily immediately. However I am sure that even the casual audience is likely to make the connection. 
The use of the name of (Pop) Fisher, the use of Knights for the team name, the use of lightning as a divine (or otherwise) signaler and the use of Wonder Boy as a sort of Excalibur are further connections.

It is interesting to point that the involvement with the wrong women is what causes the king's wound in a pragmatic manner (a -silver- bullet, its complication over years... and apparent poison, even if only implied,) and not necessarily because of a sort of vague divine retribution or similar sinful taint, but simply because these women are the gateway to a direct connection to the danger elements.
However, the saving female figure (Guinevere? a stretch here, but certainly a stand in for pure, female love,) does seem to be of a magical nature, she gets a literal light halo and just the mere sight of her leads the king to his salvation, even he the king remains involved with one of the fallen woman, (who gets repudiated, but only much later.)
Thus it is not sex by itself, but wrongful choices (in women,) which generates the fall (from grace.) The hero need not be virginal or pure, simply make better choices (which he ultimately does.)

Children and childhood get constant mention and play a significant part and the movie attempts (and is successful) in casting the game of baseball as symbolic or as an equivalency of Mythic struggle for modern times.

Ultimately a happy ending generates further distance from the feeling of a fleeting Camelot or Le Morte d'Arthur. This happy ending is apparently not a part of the inspiring novel.