The bull market has been on fire this year, as 2017 has lacked volatility and stocks continue to grind higher. But there is an Achilles heel to the market and the bulls don't want to see it develop much further.

Is the market failing to reward strong results? That could crush the bulls.

Speaking on CNBC's "Stop Trading" segment Wednesday, TheStreet's Jim Cramer took a closer look at  (NSC - Get Report) . Shares are down 2.75% despite beating on earnings per share and revenue estimates. The company even set an operating expense ratio record during the quarter. Things are going really well!

The company reported a "remarkable quarter" and CEO James Squires is doing a "fantastic job," Cramer said. So why is the stock selling off? He acknowledged that Norfolk Southern stock is still trading on relatively light volume and those fortunes could reverse.

But it's a troubling sign to see a company report such a strong quarter and see its stock price move lower. The bulls want investors to say, "it's rallying because of good news and will continue to rally." They don't want investors to be underwhelmed by great results and sell the stock as a result, reasoned Cramer, who also manages the Action Alerts PLUS charitable trust portfolio.

Even more so with the railroad stocks, because these companies are such a great barometer on commerce and the overall economy, Cramer concluded. But if this view starts to be applied widely across the market, it could be bad news for the S&P 500 ETF (SPY - Get Report) , Dow Jones Industrial ETF (DIA - Get Report) and the Nasdaq ETF (QQQ - Get Report) .

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At the time of publication, Cramer's Action Alerts PLUS had no position in any companies mentioned.