Blood bowl teams have a really varied structure. Most of the dudes on any given team are strength 3 but there are exceptions - halflings, goblins, and other little critters have lower strength and a few things have strength 4. However, most teams have access to one dude with strength 5 who usually has some other major drawback to compensate for being so large and in charge. They are called Big Guys collectively. There are a few different drawbacks:
1. Bonehead: Lose your action 1/6 of the time.
2. Really Stupid: Lose your action 1/6 of the time always, 1/2 of the time if nobody smart is nearby.
3. Wild Beast: Lose your action 1/6 of the time always, 1/2 of the time if you aren't attacking.
4. Take Root: Become rooted in place permanently 1/6 of the time.
These are all pretty hideous drawbacks, with Bonehead being the obviously least hideous. People still use Big Guys of course because you can play around their disadvantages and they do hit really hard but they cause real problems when you try to make a plan. Most guys have to roll dice to attack enemies or pick up / throw / catch the football but Big Guys can't even walk without checking to see if they suck this turn. It is really terrible when you rely on a dude to just stand in a place and provide a tackle zone or pin an enemy down and they just stand there instead. The real issue is that you can't make any kind of long term plan that relies on your Big Guy doing what you want. Just having one around adds a large amount of uncertainty to your game and mucks up plans constantly. I generally don't run them on my teams because they end up being very expensive and causing more problems than they are worth in the long run, I think.
This added uncertainty is really a problem for humans but less so for the computer. It makes plans and tries to execute them but it doesn't have the same level of awareness that a really good human player does. A human is often going to be completely boned when a Big Guy doesn't follow orders but the computer's actions are usually a lot more random and they just continue blindly swinging even if things go completely off the rails. The other thing about the computer is that it is rated to lose. It just isn't as good as a human so something really swingy like a Big Guy who sometimes is just a wrecking ball and sometimes is hopeless garbage is great for it. The more randomness the computer can introduce into the game the better off it is since if everything plays out evenly it loses nearly every time to a careful human.
My current campaign against the computer is trying to achieve a specific goal. I want to injure the entire enemy team of 16 players and have not a single enemy that can face me. I managed to get a team down to 14 injured guys, one guy ejected for cheating, and 1 guy knocked out but I couldn't manage to get that knocked out guy back onto the field to try to kill him again. It takes some serious doing to make this happen, but I have constructed a team of savage murderers to attempt it. I probably can't succeed unless playing against halflings / goblins / ogres / lizards but I will certainly keep trying. It feels very satisfying to watch elves die beneath the boots of my mutant chaos beasts.