If you aren't already, get on FUMBBL. Besides being easier to find games there, it also hosts replays of every match ever played in the engine as well as having a "spectate ongoing match" function. Lots of tactics to pick up that way.
I'm far from a pro there, been playing a few weeks with a 35% win percentage or something, but here is my understanding of light vs heavy so far:
Speedy teams win more matches but are way more fragile. If facing a speedy dodgy high AGI team, a good bashy player will go for the 2-1 grind. The 2-1 grind means gaming the rules somewhat, which is faggotassy, but it works. Basically, a bashy team will begin the match by letting you have the ball and more or less letting you score while trying to inflict as much hurt on your guys as possible and making it impossible for you to stall via the threat of killing all your guys with blocks and fouls or threatening your ball carrier. Then, once you have scored, they will use the remaining turns of the half to rumble down the field and score in the last turn of the first half. For the second half, they will receive the ball, which they will then hold on to for the entire half while pummeling the shit out of your faggot elves or ratmen, stalling like hell and scoring in turn 16, bringing the score to 2-1.
To counter this, you need to be able to do two things: Score enough to make such playing-it-safe strategies ineffective and keep your guys from getting too close and personal with enemy players with superior armour, strength and blocking skills. You can keep your guys safe by playing to your strengths: High agility and dodging skill. As your guys will get smoked in a stand-up fight, make a 1 tile dodge away from the bruisier players you don't want to fuck with. As they can only make 1 blitz per turn, all but 1 of your guys can then avoid getting pimpslapped, and the tackle zones of your dodgy characters will hinder the mobility of the opposition as much as if you'd been marking them by standing next to them. Do this well enough and you may be able to prevent the slower bashers from scoring for long enough to make the 1st half end 1-0 or alternatively blitz them for the ball and end the half 2-0. I tend to play orcs, so I can't really comment more specifically on good elf-scoring tactics, but many people here are Pro Bros and should be able to help you out.
BB is a pretty tough game with a lot of potential for RAEG! when the dice fuck you over. Thing is, good players will beat bad players 9/10 times by minimising the impact of the dice, which is the entire charm of the game, really. Expect to lose a hell of a lot before stuff begins making sense. I'm now at the point where I can draw as many matches as I lose, now I just gotta figure out how to convincingly WIN without using bitch tactics.
Also, read this website, it's really good:
http://bbtactics.com/