To add a little more to this thread, I've been using my new D3200 for skateboarding/BMXing at my local skatepark, something I have done before but not put so much thought into. It was bright daylight so the kit lens was fine, and I used a 0.5x wide-angle adapter for most of it, but anyway:
Focus mode - Generally this would be set to AF-A (Auto-servo AF) so the camera does its best to adapt to the situation, but if you know you are shooting fast moving objects such as skateboarders/footballers then Dynamic Area (Continuous-servo AF) will be better. "Focus area does not lock when shutter-release button is pressed halfway.", instead it will continue to auto-focus right up to the split-second you pick your shot.
AF-area mode - I usually have this set to Single Point so I'm in control, but when shooting moving subjects it will be best to switch to Dynamic Area AF. This means it will be weighted according to where your spot is; but if the subject leaves that spot the camera will notice and focus to the left/right/top/bottom instead; trying to follow the subject in real time. This is particularly useful for skateboarding as I was shooting with the camera at arms length; not looking through the viewfinder, while I am moving; and the subject is moving very very quickly too; I was guesstimating the direction to point in and trying to get the camera as close to the action as safely possible. This is to avoid getting shots where camera decided to focus on the background instead of your subject.
So my routine now is that for normal use I'd have Auto-servo AF and Single Point AF, but if I was doing action sports then I'd switch to Continuous-servo AF and Dynamic Area AF.
I've got a monopod as well and never use it, but then I don't have a ball-head yet .. I reckon monopods are best when shooting distance with a long focal length; like exactly your example of a photographing footballers from the sidelines.
I'm by no means experienced, am I talking sense? Comments? Suggestions?