Under Armour Short Interest Rises to 35.5%

Welcome to this week's installment of "The Short Interest Report" - The Fly's weekly recap of short interest trends among some of the most widely followed high-short-float stocks. Using the data from our partner, which utilizes the latest information from stock lenders to estimate short interest changes for thousands of publicly traded companies, this report will screen for some of biggest changes in short interest as a percentage of free float and days-to-cover ratios while also considering the short interest data on some of the more volatile and heavier-traded names of the week. Based on the availability of data from Ortex, the report tracks the trading period that covers prior Friday through Thursday of this week, excluding holidays. As a basis of comparison for stocks discussed below, the S&P 500 index was up 0.3%, the Nasdaq Composite was up 0.2%, the Russell 2000 index was up 2.7%, the Russell 2000 Growth ETFwas up 2.7%, and the Russell 2000 Value ETFwas up 2.9% in the five-day trading session range through January 15.SHORT INTEREST GAINERSOrtex-reported short interest on Under Armourhas been on a steady uptrend throughout the second half of 2025, rising from below 15% level in late June of 2025 to above 30% by mid-December. The final week of December and the first week of January had seen the growth in bearish positioning flatline, but this week, short interest as a percentage of free float on Under Armour hit record highs, spiking from 29.3% to 35.5%. Concurrently, elevated trading volume in the name resulted in days-to-cover on Under Armour falling from 7.9 to 7.1 - a three-week low. The stock traded down 4.0% in the five-day period covered through Thursday, though shares were up nearly 50% from late November trough and are still up 16% year-to-date in 2026.Ortex-reported short interest in United Parks & Resortstroughed at a two-month low of 19.2% on November 20, matching the 2025-low for the stock price. A 5% passive stake disclosed by Golden Tree Asset Management since then has helped the stock price bounce back, with shares now up 28% from those lows, though bearish positioning on the name has also tracked the higher stock price to the upside. This week, short positioning as a percentage of free float on the name accelerated its rise, gaining from 23.2% to a multi-year high of 27% while matching the exchange short interest data, which reached that level as of December-end. The stock was up 3.3% in the five-day period covered and has now gained 4.3% in 2026.Staying with the theme-park theme, Six Flags Entertainmenthas also seen an uncharacteristically steep bounce in bearish positioning in concert with a rebound in the stock. Ortex-reported short interest on the name has similarly reached an intermediate low in mid-November around 19%, matching the 2025 lows in shares, and the rebound in the stock has been comparably steep. Short position as a percentage of free float in Six Flags was up from 21.5% to 24.5% - a multi-month high. The stock, meanwhile, was up 3.9% in the five-day period covered, with shares up a similarly dramatic 32% from its November lows.Ortex-reported short interest on Celcuityhad troughed at a three-month low below 20% in the final week of November, followed by a gradual ascend that also included a one-point of 23.7%-24.7% from December 10 through the first week of January. This week however, the bears are showing more resolve, with shorts as a percentage of free float jumping from 23.7% to 28.8% - a two-month high. Days-to-cover on the name rose from 4.4 to 4.9 despite steady volume to start 2026. The stock has had a strong start to 2026 with a 7.2% gain, though in the five-day period covered, Celcuity was up just 0.6%, also registering an outsized loss on Thursday.SHORT INTEREST DECLINERSOrtex-reported short interest in NuScale Powerhas been on the back foot since mid-November as bears have largely been booking profits into year-end with shares moving decisively lower. A bounce in the stock price to start the year however has only brought on more covering among the shorts, and this week, bearish positioning as a percentage of free float was down from 25.4% to 21.8% - the lowest level since November 24 and within two percentage points of a five-month low. The stock was down 3.9% in the five-day period covered through Thursday of this week, but year-to-date, NuScale Power is up 42%.