Getting a TeleConverter for Sports?

So I've been wondering, especially for summer baseball, soccer and football, how accurate would a 1.4x teleconverter with a 70-200 2.8L be on AF speed for these sports?

Not sure about "accuracy" but - do keep in mind that you will lose a stop of light with a 1.4x converter, and that may make a difference in capturing an action shot or getting blur. Just an FYI, I guess.

I used it last summer for baseball. It did well on the lens. As long as it is outdoor with lots of light I think you will be fine.

AF speed will suffer from the TC. If you plan on shooting fast moving subjects, it would be better (though more expensive) to get a dedicated longer prime.

I have used a 1.4 on my 70-200 and it works fine. Maybe a slight difference in AF speed, but nothing to make a big difference. IQ is still very solid as well

It may work OK for younger aged soccer players (slower speed of play), but I have tried it with my 70-200 f/2.8L for high school aged soccer and found the decreased AF performance to be insufficient. My keeper ratio suffered greatly with a 20D. I haven't used the TC for a quite some time and frankly, do fine without it.

I have also tried it for baseball/softball for shooting batters where I used it on a tripod with a remote to trip the shutter and I could pre-focus on a batter and it did fine. It just didn't track fast moving subjects well enough.

JMHO.

Regards,
Jeff

Now that taxes have come back and I have $$ aside, I'll respond to this.

I will be using it to shoot soccer, baseball and football. I'm upgrading to a 70-200 F/2.8 non IS in about two months. Does anyone have experience with this combo on a 40D, Mark II or Mark III?. I know that AF speed/accuracy has improved a lot in the new models.

Also, has anyone tried this combo at night (thinking night ball games). I was able to shoot with my 70-200 F/4 last week at ISO3200 without much of a problem, except for having to crop a lot.

I have used it on a 1D2 with no problems. I did not find that the AF was insufficient at all. I have also used it for night football games and it did great.

I use the 1.4x TC on my 40D and 70-200 f/2.8. Still find the focus plenty fast enough while the f/4 still works for an apeture.