Tag n Bag is describes the broad Corporation strategy of tagging the Runner and then doing enough Meat Damage to Flatline them (causing the Runner to immediately lose the game, and the Corp player to win).
SeaScorch is one very common Tag n Bag strategy using two Core Set cards - Scorched Earth and SEA Source. However other strategies exist, using cards such as Posted Bounty and Midseason Replacements to tag the runner, and/or cards such as Private Security Force and Dedicated Response Team to do the meat damage.
Punitive Counterstrike is another card that is used to flatline the runner using meat damage. Technically it is not a Tag n Bag strategy since it does the damage without ever tagging the runner, but thematically and mechanically it is related.
There are two main variants of runner counter-strategy - to avoid getting tagged, or to prevent the meat damage.
Tags can be avoided directly with cards like Decoy or New Angeles City Hall. If the runner suspects the tag will be placed via SEA Source or Midseason Replacements they can protect against this by keeping more credits in their pool than the Corp, but this will not stop a tag from Breaking News or Posted Bounty.
Preventing meat damage is almost always done by including multiple copies of Plascrete Carapace in a deck, and installing them as soon as possible when a Tag n Bag strategy is suspected.