I do not get the meaning of this sentence.

No, it means that they have persevered to play, and the evidence of their perseverance is that they play at all. Without more context, it is difficult to answer this question. Who are "they?" What do they play, musical instruments, as a team in a sporting event?

Thank you.
I should have put more context. Here.

"Their nervous twitchiness gives them real trouble when catching the ball.It is a testament to their enthusiasm and perseverance that they can play at all, and they do play pretty well."

They are (some how) team in sporting event.

So, it's mean...
"It is evidence that they have perseverance to play the sports game"?

Are they have perseverance even though they are nervous guys ??

Let us say, rather, "That they play the game at all is evidence that they have persevered"--it will read better in English.

You would ask: "Do they have perseverance, even though they are nervous guys?" Yes, and that's the point. They have persevered, and the evidence that they have is that they have overcome their nervousness, and played the game despite being nervous.

So,they are not good at sports but with perseverance,they overcome nervousness.
Hmmm sounds good.

Thank you!
was very helpful.