Horse Boot is one of the three skins released in the Shamrock's Gang part of the St. Patrick's Day offer. It could be purchased individually with game coins in mid March 2017.
Horse Boot could be purchased in the Skins Shop under the 'St. Patricks Day' tab for 690 coins. This skin was available for a limited time and may not be available for purchase in the future.
Details of this skin may vary depending location, platform or time.
Note: The Shamrock's Gang sub-offer was released again for a limited time in mid March 2021. The price for Horse Boot remained at 690 coins for this release.