Spartacus: Blood and Sand S1E3 and 4

In E3, the gladiators' training begins in earnest with much grunting, sweating, bashing about with practice swords and lifting of heavy things.  Spartacus is not much getting along with Crixus the Undefeated, Batiatus's prize gladiator (and Batiatus's wife Lucretia's occasional sex toy).  But Spartacus is determined to make a go of it, especially since Batiatus told him that he'll need much money to buy his wife's freedom, once Batiatus has located her.  So when Batiatus and Lucretia organize a gladiator tournament for the city of Capua, in an attempt to curry favor with Capua's senator, both Spartacus and his new BFF Varro (who needs money to settle his gambling debts), hope to garner places in the tournament that will net them some cash.

During the pre-tournament party, the Senator's hedonistic and snobby daughter Ilithyia develops a yen for gladiators, which includes watching with rapt attention when Lucretia orders Varro to service a slave girl in front of the guests.  Lucretia's delight at Ilithyia's delight is short-lived, however when the spoiled girl's short attention span turns elsewhere.  At the party, Spartacus learns that he and Varro are to fight in the first match, which will bring neither of them any cash, so he picks a fight with Crixus, in front of all the guests, forcing Batiatus to proclaim Crixus vs. Spartacus as the headlining fight to appease his audience.

Of course, in the tournament the next day, poor Spartacus is no match for Crixus who nearly kills him before Spartacus begs for mercy.  Batiatus grants it, sparing Spartacus's life, but the Capuan crowd is displeased at the mercy and Batiatus ends up losing a lot of money on the event.  To punish Spartacus for his major mistake, he kicks him off the gladiator team, saying that he must fight in the "underworld" until he dies or wins back favor.

S4 is Spartacus's trials and tribulations in the underworld: unsanctioned, highly-dangerous and -illegal fights to the death that take place in the catacombs beneath Capua.  It's all very ugly - the crowd especially is ugly, screaming for painful death for the combatants - and Spartacus has to dig deep to find the wherewithal to keep himself alive.  But he does, winning match after match (and gaining vicious scar after scar), and winning money for Batiatus, who sorely needs the cash to pay off his impatient bookies. 

After a time, however, Spartacus can take no more and tells Batiatus that if he will promise to rescue his wife, Spartacus will throw the fight: Batiatus should bet all he has against Spartacus; the Thracian will die; and Batiatus will make a killing.  The greedy Batiatus agrees but during the fight, as Spartacus is getting brutally pummeled, assassins make a move on Batiatus.  Knowing that a dead Batiatus will not be able to save his wife, Spartacus saves his master's life, and kills his opponent in the process.  Batiatus is in a tough position now: he's lost all the money he bet against his own man, but his life has been saved.  Troubled but grateful, he reinstalls Spartacus in the ranks of his gladiators.

In the B-plot, Crixus is not just a mass of muscles as he is secretly in love with one of Lucretia's slaves.  They must keep it hidden, however, because Lucretia (Lucy Lawless) is a jealous and vindictive woman.