You can't tame these guys by knocking them out. Instead, you need to steal their fertilised eggs (just like wyverns and rock drakes), hatch them and raise them, just a bit harder than knocking them out. The eggs can, of course, be found in their nests and do be careful while trying to steal one as the Deinonychus is very territorial. Hope this helps :)
Here's how to steal one early game: If you spawn in at chalk hills 3 and spawn next to a pond walk opposite to the pond. There are some nests right there. Snatch one quickly and run off the cliff next to the pond. Be careful and make sure to fall into the water. From there make a left and you should get to a beach area. From there it should be easy to find your base.
#1. Ride your flying mount and scout for deinos nests at chalk zone biome.
#2. Stop at high ground and wait for the parent deinos to chase something away from nest. Or use your Argentavis to carry and drop nearby Ankylo or Doedicurus as a bait to distract the guarding deinos. (Be smart! Wait for the perfect opportunity to do step #3)
#3. Approach the egg using your flying mount quickly!
#4. Jump out near the egg -> TAKE THE EGG QUICKLY -> jump in and fly away ASAP! (This must be done in less than 5sec!)
#5. Make a 4x4 thatch/any foundation with closed wall, roof and a door entrance.
#6. Place 10 standing torches inside. (Add more if the egg says "too cold")
#7. Drop the egg/s then light up the torches.
#8. Wait for the incubation to reach 0%.
*These steps are meant for beginners or first timers on snatching and hatching Deinonychus egg @ VALGUERO map. Good luck!