Discount cellular carrier Leap Wireless (LEAP) is sinking after Jefferies analyst Thomas Seltz downgraded the stock to Underperform, the firm’s lowest rating, from Hold in a note to investors earlier today. Leap's business trends were weak in 2012, and the carrier's performance will probably continue to be lackluster in 2013, Seltz wrote. Leap's competition is likely to intensify this year as Sprint (S) and T-Mobile (DTEGY) lower their prices further, Seltz believes. Furthermore, the company will have trouble reducing its spending, and its value as a takeover target is limited, added the analyst, who reduced his price target on the shares to $5 from $6. In mid-morning trading, Leap fell 36c, or 5.69%, to $5.97.