The maintenance of a Sell rating suggests that Citigroup analysts believe that Foot Locker's stock may not perform well in the near term. However, the increase in the price target from $18 to $20 indicates a slightly more positive outlook than before, which could mean that the downside risk is not as severe as previously thought. This news could lead to mixed reactions in the market, with some investors seeing the raised target as a positive sign, while others may focus on the Sell rating, potentially leading to short-term price volatility.