"Heavy" or "Heavyweight" is a classification of gladiators who are generally more powerful but slower than most other gladiators. The Heavy gladiator classes consist of the Centurion, Cyclops, Minotaur, Ogre, Samnite, and Yeti.
Heavy classes excel in HP and Strength, but lack defense. If you have a Light Class character such as a secutor or a bandit you will have a high advantage in defense, making you somewhat untouchable. If you're Light Weight character is low on health you can use skills like Sand Toss (a Secutor skill) or Incapacitate Enemy (a Bandit skill) to gain an advantage. If you have a Light Weight character it's recommended to backstab a Heavy Weight and perform twice as much damage.
If you are playing as a Medium Weight class you will have a disadvantage against them. If available, use Empower Self to increase accuracy, defense, and damage. If available it is recommended to be on a higher elevation to increase damage, so if there are crates on the battlefield use them to you're advantage. And if possible, attack from behind to increase the damage dealt.
Greater Bears, Greater Cats, and Greater Wolves are treated as a Heavy class in respect to other gladiators. Greater beasts cannot be recruited but it is useful to know that they have an advantage over Medium classes (including Bears, Scorpions and Scarabs ) and are more vulnerable to Light classes (including Wolves and Plains Cats).