Question: Which sport includes Popular formations include the 4-2, 6-2, and 5-1 systems?
About the article "Volleyball", section "Team play".

Candidate passages:
The three standard volleyball formations are known as "4–2", "6–2" and "5–1", which refers to the number of hitters and setters respectively.
4–2 is a basic formation used only in beginners' play, while 5–1 is by far the most common formation in high-level play. 
Volleyball is essentially a game of transition from one of the above skills to the next, with choreographed team movement between plays on the ball.
These team movements are determined by the teams chosen serve receive system, offensive system, coverage system, and defensive system.
The serve receive system is the formation used by the receiving team to attempt to pass the ball to the designated setter.
Systems can consist of 5 receivers, 4 receivers, 3 receivers, and in some cases 2 receivers.
The most popular formation at higher levels is a 3 receiver formation consisting of two left sides and a libero receiving every rotation.
This allows middles and right sides to become more specialized at hitting and blocking.
Offensive systems are the formations used by the offense to attempt to ground the ball into the opposing court (or otherwise score points).
Formations often include designated player positions with skill specialization (see "Player specialization", below).
Popular formations include the 4-2, 6-2, and 5-1 systems (see "Formations", below).
There are also several different attacking schemes teams can use to keep the opposing defense off balance.
Coverage systems are the formations used by the offense to protect their court in the case of a blocked attack.
Executed by the 5 offensive players not directly attacking the ball, players move to assigned positions around the attacker to dig up any ball that deflects off the block back into their own court.
Popular formations include the 2-3 system and the 1-2-2 system.
In lieu of a system, some teams just use a random coverage with the players nearest the hitter.
Defensive systems are the formations used by the defense to protect against the ball being grounded into their court by the opposing team.
The system will outline which players are responsible for which areas of the court depending on where the opposing team is attacking from.
Popular systems include the 6-Up, 6-Back-Deep, and 6-Back-Slide defense.
There are also several different blocking schemes teams can employ to disrupt the opposing teams offense.
Some teams, when they are ready to serve, will line up their other five players in a screen to obscure the view of the receiving team.
This action is only illegal if the server makes use of the screen, so the call is made at the referees discretion as to the impact the screen made on the receivers ability to pass the ball.
The most common style of screening involves a W formation designed to take up as much horizontal space as possible.
The most popular college sports, measured by NCAA reporting on varsity team participation, are: (1) football (64,000), (2) baseball/softball (47,000), (3) track and field (46,000), (4) soccer (43,000), (5) basketball (32,000), (6) cross-country running (25,000), and (7) swimming/diving (20,000).
The most popular sport among female athletes is soccer, followed closely by track and field.
Among organized high school sports, the sports with the highest number of participants are: (1) football, (2) basketball, (3) track & field, (4) baseball/softball, (5) soccer, and (6) cross-country.
Wrestling is the sixth most popular sport for boys, while volleyball is the third most popular sport for girls.
Popular high school sports in various regions of the U.S. include the Texas High School Football championships, the Indiana Basketball championships, and ice hockey in Minnesota. 
Examples get quite complicated quickly, here are small examples:"n" = "n" (by rule 1) "p→q" = "pq" (by rule 2) Thus 3→4 = 34 = 81 1→("any arrowed expression") = 1 since the entire expression eventually reduces to 1number = 1.
(Indeed, any chain containing a 1 can be truncated just before that 1; e.g.
"X"→1→"Y"="X" for any (embedded) chains "X,Y".)
4→3→2 = 4→(4→(4)→1)→1 (by 4) and then, working from the inner parentheses outwards, = 4→(4→4→1)→1 (remove redundant parentheses ) = 4→(4→4)→1 (3) = 4→(256)→1 (2) = 4→256→1 (rrp) = 4→256 (3) = 4256 (2) = 13 407 807 929 942 597 099 574 024 998 205 846 127 479 365 820 592 393 377 723 561 443 721 764 030 073 546 976 801 874 298 166 903 427 690 031 858 186 486 050 853 753 882 811 946 569 946 433 649 006 084 096 exactly ≈ 1.34078079299 × 10154 With Knuth's arrows: formula_192→2→4 = 2→(2)→3 (by 4) = 2→2→3 (rrp) = 2→2→2 (4, rrp) = 2→2→1 (4, rrp) = 2→2 (3) = 4 (2) (In fact any chain beginning with two 2s stands for 4.)
The usual formations of the defense are 6-0, when all the defense players line up between the 6-meter and 9-meter lines to form a wall; the 5-1, when one of the players cruises outside the 9-meter perimeter, usually targeting the center forwards while the other 5 line up on the 6-meter line; and the less common 4-2 when there are two such defenders out front.
Very fast teams will also try a 3-3 formation which is close to a switching man-to-man style.
The formations vary greatly from country to country, and reflect each country's style of play.
6-0 is sometimes known as "flat defense", and all other formations are usually called "offensive defense".