This question is a little vague, so I'm going to have to make some assumptions.
- This is in Sun/Moon, meaning that the Riolu is being encountered at level 52.
- You are using a standard Poké Ball.
- Riolu is not affected by a status condition.
- Riolu is at 2% of its HP.
Using the Catch Rate Calculator for Gen VI (although the standard Poké Ball catch rate is unchanged in Gen VII), a Riolu under these conditions has a catch rate of 39.577%.
With False Swipe your odds rise a tiny bit, up to 39.758%.
If you Paralyze this Riolu, the catch rate rises to 53.644%.
With False Swipe, it rises to 53.885%.
