5 things we learned from 49ers preseason win vs. Cowboys

The 49ers appear to have made a draft-day steal April when they selected linebacker Dre Greenlaw in the fifth round. In the 49ers preseason opener, the rookie showed why the team coveted him coming out of Arkansas.

Greenlaw is fighting for the starting job at the SAM linebacker spot. As training camp progresses, he has shown little evidence of the label he was given as lacking what it takes to be a game changer in the NFL.

There are some areas Greenlaw will need to shore up if he hopes to on the starting defense in Week 1 of the regular season. Most notably, he will need to get better at not biting on play action, as he did a few times Saturday night. He was also hit with a roughing-the-passer penalty. Greenlaw will need to learn to harness his aggressiveness at this level so as not to draw penalties and the ire of his coaches.

Aside from that, the former Razorback was constantly around the ball. He ended the game with five tackles on 43 total snaps. One that stood out was a tackle on running back Darius Jackson in the second quarter. Greenlaw sniffed out the run, shot the gap and went untouched into the backfield where he dropped Jackson for a 4-yard loss.

It would be no surprise to see this rookie starting in Week 1.