The hit and run attacks are quick attacks that may last only for a few seconds before ending. They are usually followed a few minutes later by another attack for a similar length of time.
They are quick attacks that are usually repeated several times before ending that has a small amount of time between each attack. The attacker may replace the units he used with different types depending on the situation.
What leads to their success is that the units get time to heal between attacks ad then go into battle and cause more damage to the attack. To add into that, the attacker gets extra knowledge on his enemy's base, allowing him to get units that will be the most powerful against the opponent.