Stocks kicked off the first full week of September with a split decision Monday. Hurt by broad weakness in oil stocks, the S&P 500 fell 0.3%. The energy sector has a 10% weighting in the benchmark index. Half of the day’s 10 worst-performing industry groups were oil related. Crude oil for October delivery dropped 63 cents to $92.66 a barrel, the third straight loss. The Nasdaq rose 0.2% in a seesaw session.