A. The blower:
The person who is blowing the Shofar is required to stand during the blowing. It is therefore forbidden for him to lean on any item in a way that it supports him from falling. If one transgressed and blew the Shofar while sitting he nevertheless fulfills his obligation and is not required to repeat the blows in a standing position.
B. The congregation:
The congregation which is listening to the Shofar blowing is not required to stand during the blowing. This applies even if they have not yet fulfilled their obligation of hearing Shofar and are fulfilling it with the current blowing. [Nevertheless, the custom is to stand while hearing Shofar.]
Tekios Meumad: The above ruling that the congregation is not required to stand only applies to the Tekios that are not blown during Musaf. However by the Tekios blown during Musaf both the Baal Tokeia and the listeners must stand while the Shofar is being blown. [However Bedieved one fulfills his obligation even if he remained seated.]
C. The blessings:
The blessing is recited in a standing position. [Some Poskim rule that even the listeners are to stand at the time of the recital of the blessing. However others rule that it is not necessary for the listeners to stand for the recital of the blessing and so is the custom of certain communities.]
The blessing is recited in a standing position. The Baal Tokeia must stand while blowing the Shofar. The custom today is that also the congregation stands for the blowing.
If one already fulfilled his obligation and is blowing on behalf of another, must he stand during the blowing?
Some Poskim rule that in such a case the Baal Tokeia may be seated while the listener is to stand.
 581/1; Michaber 585/1
 The reason: This is learned from a juxtaposition of the verse “A day of Teruah it is Lachem” and “Usfartem Lachem”. It is expounded that just like the counting of the Omer must be done standing, so too the blowing of the Shofar must be done standing. [ibid; Tur 585; Hagahos Maimanis; Beis Yosef 585] This is a tradition from our forefathers. [Kesef Mishneh brought in Birkeiy Yosef 585/1]
 Admur ibid; Drashos Mahril Shofar; Darkei Moshe 585; M”A 585/1; Peri Chadash 585; Elya Raba 585/1; Birkeiy Yosef 585/4; Shaareiy Teshuvah 585/1; Chayeh Adam 141/6; M”E 585/5; M”B 585/2; Kaf Hachaim 585/4
The reason: As in such a case this leaning is not defined as standing but as leaning. [Admur ibid; See also 607/7]
 Admur ibid; M”A 585/1; Peri Chadash 585; Elya Raba 585/3; Birkeiy Yosef 585/2; Shaareiy Teshuvah 585/1; Chayeh Adam 141/6; M”E 585/5; M”B 585/2; Kaf Hachaim 585/5
The reason: As the above obligation to stand is a merely Rabbinical enactment. [Admur ibid] As even the requirement of counting the Omer in a standing position, which is the source of the requirement to stand by blowing Shofar, is a merely a Rabbinical enactment. [489/4]
Other opinions: Some Poskim rule that even the listeners are included in the juxtaposition of the above verse and hence they must stand. However they hold that the Tekios Meumad is the fulfillment of the main Mitzvah of Shofar, and not Tekios Meyushav, and hence by Meyushav they may sit. [Radbaz 1/25; Mor Uketzia 585; Elya Raba 585/2; Mateh Yehuda; Machazik Bracha 585/1; Erech Hashulchan 585/1; Shaareiy Teshuvah 585/1; Kaf Hachaim 585/2] This reason is clearly negated by Admur here and in 124/7 and 592/7 which explains that the main Mitzvah is fulfilled by Tekios Meyushav.
 Admur ibid; M”A 585/1 in name of Kneses Hagedola in negation of Radbaz ibid brought in M”A
Other Opinions: Some Poskim rule that in such a case even the listener must stand, as explained in the previous footnote. [Radbaz ibid, brought in M”A ibid; Shulchan Gavoa 585/3; Birkeiy Yosef 585/3; Shaareiy Teshuvah 585/1; M”E 585/5; M”B 585/2; Kaf Hachaim 585/3] The M”A ibid however questions this ruling of the Radbaz and Admur omits it completely in 585/1-2. See previous footnote.
 M”B 585/2
 Admur 585/1; 592/2; Levush 585/1; M”A 592/1; M”B 592/2; Kaf Hachaim 592/3
 The reason: The reason for this is because the congregants are required to stand during Chazaras Hashatz. [Admur 124/7 in parentheses going according to the opinion that requires standing by Chazaras Hashatz. However see Piskeiy Teshuvos 124/10 that today many are lenient to sit by Chazaras Hashatz.]
Other reasons: Some Poskim rule that the reason one is required to stand for the Tekios Meumad is because even the listeners are included in the juxtaposition of the above verse and since the Tekios Meumad is the fulfillment of the main Mitzvah of Shofar, therefore also the listeners must stand. [Radbaz 1/25; Mor Uketzia 585; Elya Raba 585/2; Mateh Yehuda; Machazik Bracha 585/1; Erech Hashulchan 585/1; Kaf Hachaim 585/2] This reason is clearly negated by Admur in 585/1-2; 124/7 and 592/7 which explains that the main Mitzvah is fulfilled by Tekios Meyushav.
 P”M 592 A”A 1; M”B ibid; Kaf Hachaim ibid
 585/4; M”E 585/3; M”B 585/1; Kaf Hachaim 585/1; See Admur 8/3 that all Birchas Hamitzvos must be said standing; Regarding standing by the blessings of Megillah reading see: M”A 690/1; Elya Raba 690/1; P”M 690 A”A 1; Beis Oved 690/9; Rameh 102; M”B 690/1
 Kaf Hachaim 585/1; Machatzis Hashekel on M”A 690/1 regarding Megillah; Beis Oved 690/9 brought in Kaf Hachaim 690/2; Shaareiy Tziyon 690/1; Vetzaruch Iyun as to the opinion of Admur in all this, as in 585/2 Admur rules that the people fulfilling the Mitzvah of Tekiah do not have to stand, despite the fact that the person blowing the Shofar has to stand. No mention is made that they have to stand while reciting the blessing. Vetzaruch Iyun.
 The reason: As the listener is considered like the reader “Shomeia Keoneh” and hence is required to stand just like the reader which is saying the blessing. [ibid]
 Ben Ish Chaiy Netzavim 15 brought in kaf Hachaim 585/1; See also Yifei Laleiv 2/2; Kaf Hachaim 690/2 that so was custom of the Beis Keil shul in Jerusalem; Mikraeiy Kodesh brought in Piskeiy Teshuvos 690/1
 Yaavetz in Siddur; Kaf Hachaim 585/5; however according to Admur ibid it is clear that the listener does not need to stand.