Todd Gurley - 6-0 5/8, 222, 4.45
Melvin Gordon, 6-0 5/8, 215, 4.52
TJ Yeldon, 6-1 1/4, 226, 4.61
Ameer Abdullah, 5-8 3/4, 205, 4.6
Tevin Coleman, 5-11 3/8, 206, 4.46
Duke Johnson, 5-9 1/8, 207, 4.54
Devin Johnson, 6-0 5/8, 224, 4.5
Matt Jones, 6-2 3/8, 231, 4.61

That's just the guys drafted in the 1st 3 rounds.

Jamaal ran an 11.10 in the 100 meters in 2014.

Just to get an idea of track speed vs. football speed (I was looking at 2014 draft results), Dri Archer, who ran a 4.26 in the combine, ran a 10.49 in HS in the state finals of the 100 meter sprint.

Jerick McKinnon of Georgia Southern (now Vikings) ran a 4.41 40 in the combine, and an 11.05 in the 100 meters as a college junior. He's 5-8 7/8, 209 lbs. as measured at the combine.

Damien Williams of Oklahoma ran an 11.17 wind-aided 100 meters as a HS junior, and a 4.45 40 yard dash at 5-11 1/4, 222 in the combine. Very likely, he was quite a bit smaller as a HS junior.

There's no reason to think Jamaal doesn't have the size or speed to play in the NFL.