Saying he wants to change a culture in youth sports where kids are encouraged to “suck it up” after sustaining head injuries, President Barack Obama on Thursday said it was time coaches and athletes started thinking about better ways to keep kids safe on playing fields. Obama said he could recall instances during his own days in Pop Warner leagues when a particularly hard hit left him sidelined for a spell. “There were a couple of times where I’m sure that that ringing sensation in my head and the need to sit down for a while might have been a...