when you 'stretch' a hit and get thrown out at second or third, you still get a 'hit' too. *single or double depending on where you get thrown out.
sac flies don't count as an AB or a hit. so, it wouldn't be responsible for a BA>OBP situation.
BA
http://m.mlb.com/glossary/standard-s...atting-average
sac flies
http://m.mlb.com/glossary/standard-stats/sacrifice-fly
obp:
http://m.mlb.com/glossary/standard-s...ase-percentage