Question: Which battle resulted as a conflict between the United States Army and the Sioux and involved a Hunkpapa Lakota holy man who was killed by Indian agency police on the Standing Rock Indian Reservation?

Context articles: Post at Grand River Indian Agency
Sitting Bull College
Standing Rock Indian Reservation
Sitting Bull
Crow Indian Reservation
Dakota Access Pipeline protests
Indian agency police
Battle of Pease Bottom
Prairie Knights Casino and Resort
The Standing Rock Rural Water System

Post at Grand River Indian Agency was a Federal military post at the Grand River Indian Agency between 1870 and 1875 in the Dakota Territory.
 It was located at the Missouri and Grand Rivers, near modern Wakpala, Corson County, South Dakota within the Standing Rock Indian Reservation.
Sitting Bull College is a tribal college in Fort Yates, North Dakota.
 It was founded in 1973 by the Standing Rock Sioux tribe of the Standing Rock reservation in south-central North Dakota.
 The Standing Rock Indian Reservation consists of a land base of 2.8 million acres in North Dakota and South Dakota.
 The SBC campuses are located in Fort Yates, ND and McLaughlin, SD.
 It is one of 34 tribally controlled colleges nationwide.
 Sitting Bull College serves as the primary educational institution on the Standing Rock Reservation.
The Standing Rock Indian Reservation is located in North Dakota and South Dakota in the United States, and is occupied by ethnic Hunkpapa Lakota, Sihasapa Lakota and Yanktonai Dakota.
 The sixth-largest Native American reservation in land area in the US, Standing Rock includes all of Sioux County, North Dakota, and all of Corson County, South Dakota, plus slivers of northern Dewey and Ziebach counties in South Dakota, along their northern county lines at Highway 20.
Sitting Bull (Lakota: Tȟatȟáŋka Íyotake ] in Standard Lakota Orthography, also nicknamed "Húŋkešni" ] or "Slow"; c. 1831 – December 15, 1890) was a Hunkpapa Lakota holy man who led his people during years of resistance to United States government policies.
 He was killed by Indian agency police on the Standing Rock Indian Reservation during an attempt to arrest him, at a time when authorities feared that he would join the Ghost Dance movement.
The Crow Indian Reservation (est. 1868) is the homeland of the Crow Tribe of Indians of the State of Montana in the United States.
 The reservation is located in parts of Big Horn, Yellowstone, and Treasure counties in southern Montana.
 It has a land area of 3,593.56 sq mi (9,307.27 km²) and a total area of 3,606.54 sq mi (9,340.89 km²), making it either the fifth or sixth largest reservation in the country.
 (Rankings are switched with the Standing Rock Indian Reservation depending on whether water areas are counted.)
 Reservation headquarters are in Crow Agency.
The Dakota Access Pipeline protests, also known by the hashtag #NoDAPL, are grassroots movements that began in early 2016 in reaction to the approved construction of Energy Transfer Partners' Dakota Access Pipeline in the northern United States.
 The pipeline was projected to run from the Bakken oil fields in western North Dakota to southern Illinois, crossing beneath the Missouri and Mississippi Rivers, as well as under part of Lake Oahe near the Standing Rock Indian Reservation.
 Many in the Standing Rock tribe consider the pipeline and its intended crossing of the Missouri River to constitute a threat to the region's clean water and to ancient burial grounds.
 In April, Standing Rock Sioux elder LaDonna Brave Bull Allard established a camp as a center for cultural preservation and spiritual resistance to the pipeline; over the summer the camp grew to thousands of people.
Indian agency police were policemen hired by United States Indian agents during the late 19th and early 20th centuries and assigned to a Native American tribe.
 It was the duty of Indian agency police to enforce federal laws, the laws of the state where their reservation was located, and the terms of the federal treaties with their tribal authority.
The Battle of Pease Bottom, also called the Battle of the Bighorn River was a conflict between the United States Army and the Sioux on August 11, 1873 along the Yellowstone River opposite the mouth of the Bighorn River near present-day Custer, Montana.
 This was former Crow Indian country altered into U.S. territory on May 7, 1868.
 The main combatants were units of the 7th U.S. Cavalry under Lieutenant Colonel George Armstrong Custer, and Native Americans from the village of the Hunkpapa medicine man, Sitting Bull, many of whom would clash with Custer again approximately three years later at the Battle of the Little Big Horn in the Crow Indian Reservation.
Prairie Knights Casino and Resort is a casino and lodge located near Fort Yates, North Dakota, on the Standing Rock Indian Reservation and about 50 miles south of Bismarck-Mandan.
 It is operated by the Standing Rock Indian Tribe.
 The casino offers high stakes gaming options, along with 725 slot machines, blackjack, craps, among other games.
 The lodge portion of the casino consists of 200 guest rooms.
The Standing Rock Rural Water System (RWS) is a $30 million water system funded by the American Recovery and Reinvestment Act in 2009 for about 10,000 residents of the Standing Rock Sioux reservation in North Dakota.
 The RWS includes the Standing Rock Water Treatment and the "Indian Memorial Intake Pump Station, a raw water pipeline, two transmission pipelines and Kline Butte Storage Reservoir."
 The main regulation reservoir of the Standing Rock Rural Water System is the $3.6 million Kline Butte Storage Reservoir, located southwest of Kenel, South Dakota, which consists of a 5 million gallon ground storage reservoir.
 Currently, (in December 2016) the intake valve for the water system is "located in a shallow part of the Missouri River near Fort Yates, North Dakota, roughly 20 miles from the planned river crossing of the controversial Dakota Access Pipeline also known as the Bakken pipeline.
 The Bakken oil pipeline Dakota line is to be "buried 92 feet below the riverbed in hard clay."
 A new valve came online in 2016 in Mobridge, South Dakota which is seventy miles south of the proposed Bakken Pipeline Missouri River crossing.
 This Mobridge intake valve is intended to service the entire Standing Rock Sioux reservation.