Oh, this 83 page paper is talking about long-short momentum strategy.

Key point: "[This strategy] tends to crash when the market rebounds after a severe market downturn. In these situations, the market risk exposure of the long-short momentum strategy is strongly negative, implying low returns in form of crashes when the market rises."

If the strategy crashes when the market goes up sharply, then it is the short leg that loses money, big time. Right?

Ah, they say it explicitly later on:
"Following market downturns, the short leg contains the most severe recent loser stocks. When the market rebounds, the loser stocks sharply increase in value."

Yeah, if you are short a stock that is zooming upward, you are going to get your head handed to you.
I think Jim has mentioned that coming off the bottom it is the stocks that lost the most which now gain the most.

Easy way to avoid that is to do just the long part and don't do any shorting.

Done and done.

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If you use BRAVE browser on the MSN (Marketwatch) link you get the whole article complete with graph. marketwatch.com - Stocks for momentum traders to consider buying and to avoid or sell short

He says the momentum is price 1 year ago vs. the 52 week high. The standard measurement we use is price 1 year ago vs. current price.