How many players are in the water, and how do substitutions work?

Q: How many players are in the water, and how do substitutions work?

Under USA Water Polo Rule WP 5: Each team starts with seven players in the water, one of them a goalkeeper in a red cap. After the game starts, a team may choose to play seven field players with no goalkeeper. Players can be substituted at any time ("flying substitutions"): the player leaves at the team's re-entry area and the substitute enters once the player has surfaced there, or both players touch hands in the water in the team's lateral substitution area. Substitutes can enter from anywhere between periods, after a goal, during a timeout, or to replace a bleeding or injured player. No substitutions are allowed between the award of a penalty throw and the throw being taken. A goalkeeper who is substituted out can only come back in as goalkeeper. At USA Water Polo national championships, a 14U team needs a rostered coach and 7 eligible players ready at game time or it forfeits 5-0. Junior Olympics zone qualifying rosters can list up to 18 athletes.

Question

Accepted Answer

Under USA Water Polo Rule WP 5:

Each team starts with seven players in the water, one of them a goalkeeper in a red cap. After the game starts, a team may choose to play seven field players with no goalkeeper.
Players can be substituted at any time ("flying substitutions"): the player leaves at the team's re-entry area and the substitute enters once the player has surfaced there, or both players touch hands in the water in the team's lateral substitution area.
Substitutes can enter from anywhere between periods, after a goal, during a timeout, or to replace a bleeding or injured player.
No substitutions are allowed between the award of a penalty throw and the throw being taken.
A goalkeeper who is substituted out can only come back in as goalkeeper.

At USA Water Polo national championships, a 14U team needs a rostered coach and 7 eligible players ready at game time or it forfeits 5-0. Junior Olympics zone qualifying rosters can list up to 18 athletes.