Entry fragging can be done in two ways:
A) The team plays a default T-side setup for map control and the entry fragger happens to take advantage of a player pushing or getting cocky and frags them. This can lead to the second kind of entry fragging (if the frag was early in the round and the team doesn't push immediately off of it).
B) The entry fragger is the first to push onto a bombsite right after their team throws set smokes for their play.
Entry fraggers can also transition into lurking players later in the round. Lurking will be covered in another article.