ah ha! now you've entered my specialty area. if you didn't already know, the lax in my name stands for lacrosse. What I would recommend is shooting from the corners if you have access. Most of the time I shoot from the corners or the endline directly in from the corners, if I can. Here's an example of this type of shot.

As you can see , it allows you a bit of a look at the goalie as well as the shooter.
Also, if yo shoot directly from behind the goal of from a bit to the left or right, you can get some great expressions when players are charging towards the goal. here's an example of one of those type of shots.
don't forgot to shoot midline too though. This will allow you to capture the transition game, as the players bring the ball upfield. Here's an example of a midline shot.

Shooting from the midline will allow you to capture goalie saves as well.
Also, shooting from the side and a bit to the front of the goal will allow you photos from the side such as this one.
The pace of the game is VERY fast, especially with the saints. I've watched them play a lot before, and while dII is a bit more stand-still than top-tier DI and DIII teams, DII still works at a fast pace. What I would recommend is learning the game before you shoot it. You will not get good photos if you don't understand the game, because unlike other sports, you can not just focus on the player with the ball. you have to be able to anticipate passes, shots, hits, etc. It's a very challenging sport to shoot, but the intensity that is present in the game makes the reward very high if you can get those good shots. But like I said, it's VERY fast and if you usually shoot football, i recommend you just go and watch a couple games first before shooting. It's an entirely different game. I would compare it to hockey on feet, except the ball is being passed in the air and the pace is faster.
And no, the fields are not surrounded with netting. Only indoor arenas are surrounded by netting. I have never seen an NCAA field with netting on it.
So that's the advice I have for you. If you have any more questions, or are confused by any of the rules, feel free to ask. I've been playing for about 6 years. So just stay low, and keep moving around (if you have access to it). best of luck.
Oh and you'll want a 300mm (at least) maybe with a 1.4x converter on it for midline shots, and a 70-200 for behind the net, with a 70-200 with 1.4x for the corner shots.
Oh and i just remembered, they won't let you on the endline. This is a new NCAA rule. but if you ever shoot it in highschool, you can go on the endline. Just not in college.
And like I was saying about the wide-angle lens, get creative and put a box in the back of the goal if they'll allow you access. It can make for some SWEET photos. I'm going to see if my former highschool will let me do that this season.
-Brent