Thought I'd followup here. In my original post, I reported that I'd missed some shots at a volleyball game because the camera simply hesitated or balked when I tried to hit the shutter.
As suggested, I did make some tests during the last week outdoors in good light - and in those conditions, the K10D was able to focus quickly and easily with both of the lenses I'm using for volleyball (Tamron 28-75 f/2.8 XR Di, and Pentax FA 50 f/1.4). That seems to confirm my suspicion that the problem was, in good part, due to the lousy lighting in the elementary school gymnasium I've been shooting in. As I said, the problem is intermittent. I know that there are spots in the gym that are definitely more badly lit than others. I think now that the balking was probably occurring when (1) I was pointing the camera at a dead spot AND (2) my technique was less than perfect.
I can't do a thing about the dead spots, but I can try even harder to improve my technique. This last weekend, I shot five more games (300+ photos taken over two hours). In line with some of the other suggestions made (particularly by Beth Davis), I tried very consciously to make sure that I'm giving the lens time to focus, and not just mashing the shutter all the way. I've always been fairly careful about how I depress the shutter, but obviously there's room for improvement. I am happy to report that I did not miss any shots this weekend as a result of balking. And I was shooting in the same gym I'd been in the previous week when I had the problem that caused me to start the thread. The only shots I missed were during a very exciting moment when I stopped doing my job dispassionately and allowed myself to get excited about what was happening at the net. I don't do that often, but hey, my kid's on the court, and I'm human (mostly).
In this most recent outing, I used both lenses - the Tamron (which I have been using for months) and the Pentax 50 f/1.4 (with which I have less experience). I'm enclosing two shots. The grayscale shot of the girls falling to the court trying to get to the ball was taken with the Tamron: 1/250 sec, f/2.8, ISO 1600. I'm pleased with my timing, but as you can see, the slower shutter and the the higher ISO make for a noisier, less sharp image. The noise is somewhat exacerbated because I cropped the photo. The other (color) picture was taken with the Pentax lens: 1/350 sec, f/1.7 and ISO 800. It is less dramatic, but technically much cleaner. (The entire gallery can be viewed
here.)
The playoffs are coming this Saturday. Not sure if I'll bring both lenses or not, but if I decide just to use the Pentax f/1.4, at least I feel more confident now that it will respond. I just have to give it just a split second to do its job.
Thanks to everybody for the responses.
Will