He is trying to capture his opponent, who is armed with a gladius (a short sword) and shield, in the net. If he succeeds he will turn to the crowds for a verdict. Everybody will scream with excitement and point down with their thumbs. That is the sign for the net man to kill the other gladiator. A quick stab with the trident and it is over for the swordsman. It is not hard to understand why emperors sometimes employ gladiators as bodyguards or assassins.
Gladiator (Latin: "swordsman," from gladius, "sword"), professional combatant in ancient Rome. The gladiators originally performed at Etruscan funerals, no doubt with intent to give the dead man armed attendants in the next world; hence the fights were usually to the death. At show in Rome these exhibitions became wildly popular and increased in size from three pairs at the first known exhibition in 264 BC (at the funeral of a Brutus) to 300 pairs in the time of Julius Caesar (d.44 BC). Hence the shows extended from one day to as many as a hundred, under the emperor Titus; while the emperor Trajan in his triumph (AD 107) had 5,000 pairs of gladiators. Shows were also given in other towns of the Roman Empire, as can be seen form the traces of amphitheatres.
There were various classes of gladiators, distinguished by their arms or modes of fighting. The Samnites fought with the national weapons- a large oblong shield, a visor, a plumed helmet, and a short sword. In like manner the tetiarius ("net man") was matched with the secutor ("pursuer"); the former wore nothing but a short tunic or apron and sought to entangle his pursuer, who was fully armed, with the cast net he carried in his left. There were also the andabatae, who are believed to have fought on horseback and to have worn helmets with closed visors-that is, to have fought blindfolded; the dimachaeri ("two-knife men"), who fought from chariots like the ancient Britons; the hoplomachi ("fighters in armor"), who wore a complete suit of armor; and the laquearii ("lasso men"), who tried to lasso their antagonists.