The Rock type is rather risky defensively. Tied with Grass, Rock types have the most weaknesses of any type, with five. The fact that Rock-types on average have mediocre Special Defense makes it harder to survive against its weakness to Grass- and Water-type moves, which are typically Special in nature. Double weaknesses among Rock types are very common, particularly to the Fighting type. Their typically low Speed stat also makes it harder for them to outspeed sweepers.
However, as Rock types have an overall high Defense, this allows them to take physical hits and stay on the field as long as they need to. Rock-types have key resistances to Fire and Flying moves, and the type is one of only three that resists Normal, the other two being Steel and Ghost, with Ghost types being completely immune to Normal attacks.
Since Generation IV, the Special Defense of a Rock-type Pokémon is increased by 50% during a sandstorm, in addition to being immune to the damage caused by it. Furthermore, the Ability Sand Stream is used due to its previously common Ability that changes weather. Moreover, most Rock types can learn Stealth Rock, an entry hazard moves that damage opposing switch-in Pokémon based on the type effectiveness against Rock.
Rock is one of the best types offensively. Rock types can deal super-effective damage to several common offensive types: Fire, Ice, and Flying, as well as Bug. Being resisted by only three of the eighteen types (Fighting, Ground, and Steel), and the fact that only a few Pokémon have a double resistance to Rock, keeps its moves relatively effective. As Pokémon of the three types that resist Rock typically can learn Rock-type moves, this proves a quite versatile combination. Double weaknesses to Rock are relatively common, mostly due to many Pokémon which have Flying as a secondary type. In particular, Rock pairs well with Ground, since very few Pokémon naturally resist this combination, and most Rock-types can learn Earthquake to this end.
The biggest drawback of Rock-type moves is the large percentage of moves which have less than 100% accuracy; in particular, the commonly used Rock Slide and Stone Edge. Most Rock-types are physical attackers, but the few special attackers among them must contend with the extreme scarcity of special Rock-type attacks, as there are only two such moves, AncientPower and Power Gem. As Rock types typically have low Speed, they may deal a significant amount of damage with acceptable drawbacks due to the learning of Head Smash, while fast Rock types lack of this devastating move. Overall, Rock is a powerful offensive type when paired with moves of other types for coverage and accuracy.
Rock-type Pokémon, on average, have the lowest Speed of all Pokémon and of fully evolved Pokémon.
Generation III introduced the most Rock-type Pokémon of any Generation, with 12, and Generation VII introduced the fewest Rock-type Pokémon, with four.
Generation IV introduced the most Rock-type moves of any Generation, with six, and Generation VI introduced the fewest Rock-type moves, with only one.
In the first season of the anime and during much of Generation I, the Rock type was often wrongly assumed to be unaffected by Electric-type attacks. This was likely due to the fact that at the time, most Rock-type Pokémon were part Ground-type and thus immune to Electric-type moves. However, the only non-Ground Rock-type Pokémon around at the time (the then five Fossil Pokémon) were actually weak to them.
The Rock type is tied with the Grass type for the largest number of weaknesses when unpaired, with five. However, a combination of the two types (Rock/Grass) would only have four weaknesses.
Rock moves are super effective against four of the five types Grass is weak to, with Poison being the exception.
Every known Fossil Pokémon is part or solely Rock-type. This is most likely due to the placement of real fossils in rock formations, as well as the process by which fossils are created.
Generation V is the only generation that does not have a Rock-type Gym.