3) Levels of sport
There are many different levels of sport, from children's sport all the way up to senior professional/international sports.
In general, the higher the level of the sport, the harder it is to gain access.
Underage sport - Most parents want to cover the sporting events of their children. They way to see their child perform and want to be able to show off how good they are. In the modern politically correct and "sensitive" time around children, photographing children's sports event can require a little preparation. Some clubs/organisations require you to be police vetted. At the very least you should approach the club and ask permission to photograph their games. You should then also speak to the coach/manager at the start of a game. Just introduce yourself, and tell them why you are there. After that, in most cases, there will be no issues. Of course, there can be instances when some parents don't want their child's image used. Respecting their wishes can go a long way to helping. No matter what, always be polite - it will get you a lot further.
Amateur sport - Most areas have some local sporting events. Local public pitches, local sports clubs and societies. This tends to be the easiest level to gain access to photograph. Usually you can just turn up, ask permission of the team manager(s) and then shoot. Local sport tends to be more emotive. Plenty of crunch tackles, great facial expressions and such. Well worth covering. Talking to the local clubs can build up good relationships and can also be a step to gaining further accreditation in higher leagues.
Professional sport - Shooting for the press or magazine or having proper accreditation tends to be the only way to get access to these events. But, shooting these can be very rewarding (photographically speaking). You tend to get cleaner action to photograph. You also shoot in better stadia, which provides a better background for images. A full stand in the background looks better than an empty one.
Generally, the higher the levels of the sport, the easier it is to capture good images. Children tend to play swarm sports (where the whole team chases the ball), while the professional sports tend to have cleaner images with just 1-2 players involved.