I have a Canon 60D and take pictures of my son's soccer games. I have the camera in action mode with the continuous picture option on. I normally never have any issues except for the occasional blurry picture but over the last two games, over half of the pictures I take (normally about 1000), are either completely or partially out of focus. I am a camera novice so not sure if it is something with the camera settings or with me. I do notice that when I hold down the button to take pictures, it is slower than normal taking multiple pictures than normal. Hopefully someone can help me.
When you say "continuous picture" are you referring to live view mode? E.g. are you looking at the LCD screen on the back to shoot rather than looking through the viewfinder?
If so, then that's a very big part of why you're getting blurred results. Here's why:
The camera has two different focusing systems. The primary focusing system for a DSLR is the "phase-detect auto-focus" system. But it has an alternative system that it uses in live-view mode called "contrast-detect auto-focus".
Phase-detect sends light through prisms which splits the image along a line (you can't see this happening). Imagine taking a pair of scissors and cutting a photograph and then not quite matching up the two halves of the photo along the cut. As the camera focuses, the two "halves" will slide along that "cut" until they align. When the two halves are aligned the camera is focused.
But more than this... because of the way the system works, the camera can actually evaluate ALL NINE of your focus sensors at the same time and can tell which focus sensor can lock focus on the nearest target (only used if you allow the camera to auto-select focus points rather than using a single specific point) and can also tell if the subject is nearer or farther than the focused distance AND... can EVEN tell how far. So the camera knows exactly how much it needs to adjust focus and in which direction in order to achieve focus. As long as there's adequate light, the camera doesn't actually have to "hunt" for focus... it just snaps right to the focused distance immediately.
In sports mode (AI Servo), it uses "predictive" focus... meaning it analyzes the focus distance each time it has to adjust focus on a moving subject which allows it to determine if the subject is getting nearer or farther and how fast. The camera factors this information in as it adjusts focus by "predicting" what the new focus distance is likely to be as it follows them.
You can see the phase-detect system has a LOT of benefits going for it: It's fast. It knows which focus point can lock focus even when everything is out of focus. It knows which way to focus and how far. It can use "predictive" focus to figure out where the subject is likely to be next. What's not to like?
Well... in order to do this, the focus system can't be on the sensor itself. The camera has to use dedicated focusing sensors. Those sensors are on the floor of the camera. The reflex mirror inside your camera (which bounces light up into the viewfinder so you can look through the lens) has a few semi-silvered spots which let light pass through onto tiny mirrors that bounce light down into the phase-detect auto-focus sensors in the floor of the camera. But to do this, the mirror has to be down.
When you use "live view", the light has to pass all the way through to the camera's imaging sensor and THAT means the reflex mirror has to swing UP. No mirror... no ability to bounce light down into the phase-detect auto-focus sensors. That means the camera cannot use this focusing system when you shoot in "live view" mode.
So the "other" focusing system is called "contrast detect" auto-focus. This is what most point & shoot cameras use. There are no dedicated focusing sensors. This system analyzes the image looking for "edges" and then adjusts focus until it can maximize the contrast along those key edges.
It's probably easier to visualize how this works by thinking of a barcode. If you think about it, a barcode is basically a white background with some solid black stripes on it. Every point on the barcode pattern is either "black" or "white". There is no gray. If you were zoomed in very tight with a magnifying loupe looking at the barcode you'd see many "black" pixels and as you transition off a stripe and onto the white background the pixels would suddenly just switch to "white".
But imagine that you de-focus the camera a bit... now you've got a bunch of fuzzy stripes instead of nice sharp stripes. If you looked at that image under a magnifier, you'd see black pixels gradually transitioning to gray pixels which then gradually transition to white pixels as you move from the "stripe" to the "background" on the barcode. That's because the barcode isn't focused.
The camera knows that if it is focused nicely, it will get an abrupt transition from one color pattern (of the foreground subject) to a very different color of the background subject. It refers to this as "contrast". When it can maximize the difference between adjacent pixels along an edge then it has achieved focus at that point.
The downside of contrast-detection is that it requires a lot more analysis to work. Also... if the camera is out of focus, it doesn't actually know if it's focused too close or too far. It has to "hunt" and test the image to see if it's getting better or worse (remember... phase-detect focus doesn't have to hunt... it knows which way to go).
Contrast-detect focusing is typically a very slow system (much much slower than phase-detect systems.) The camera can do it faster if it has a faster CPU... but then that eats through the batteries a lot quicker (which reminds me... using "live view" in general eats through your batteries a LOT faster.)
When this phase-detect system, the speed of focus is mostly just limited to how fast the focus motors in the lens can turn and lock focus. With a contrast detect system the camera has to hunt around and do a lot of analysis.
Turn off "live view" mode and put the camera to your eye to frame and shoot. You'll get MUCH better results.
There is one last point... the lens selection can make a difference. Lenses with "USM" focusing motors (Canon's "UltraSonic Motor") are much faster at focusing (the motors are physically faster/snappier and also quieter (not that quiet is a big deal at a noisy sports game, but there are places where the photographer wants the camera to be quiet). Some lenses have focus motors that aren't particularly fast or snappy and may not be able to keep up with rapidly changing focus distances.