Mismatches are just part of football and LSU head coach Brian Kelly knows this well. And he knows if you’re not prepared to account for a mismatch, you can quickly get exposed. That’s especially true playing in the SEC, where the individual talent across the board is not only arguably the best, but the deepest. So as the season approaches and Kelly considers the contingencies, he’s not going to just be coaching as usual in the likely scenario that LSU — especially on offense — is breaking in some new or young talent that could have hiccups. “If we have a freshman tackle out there going against…