Sarah Stier/Getty Images The Buffalo Bills defense has fallen flat come playoff time over the past five years. The Buffalo Bills are clearly a championship contender, but they need their defense to deliver in crunch time. That was the assessment of NFL.com writer Jeffri Chadiha, who called Buffalo’s biggest challenge “being reliable on defense when it matters most.” Buffalo has won double-digit games in six consecutive seasons and has finished atop the AFC East five straight years. Yet, it fell