Coaches Eye or Technique (formerly ubersense). I've been using Coaches Eye for couple years with no problems and now it has a GoPro feature so looking forward to using that as well.
As mentioned above..... Hudltechnique is free on the Iphone and also use Kinovea which is a free laptop download and pretty good. Suggest trying them both since you can't beat the price.
Coaches Eye looks really good and may have to spend some money and check it out.
I agree with the comments on Coach's Eye, but for catching, I also feel that there is benefit from shooting with multiple cameras (either multiple GoPro's or a GoPro and a cell phone). One from the rear and one from the side. I combine the video into a picture in picture video using Adobe Premiere or similar software. You can then import that video in the tools mentioned above. Or, just using VLC viewer you can easily view the video frame by frame.
Sure. Here's a quick one I threw together using Adobe Premiere Pro (CC 2015). Just throw 2 videos on a sequence. Then look at their audio wave forms and find a common point on each. Next, slide one or the other until the wave forms visibly match (when zoomed in very close). This will sync the 2 files. Then adjusting the position and zoom of each videos, you get the following. Finally, trim both ends of the videos and add some fading. Within Premiere Pro, there are presets you can use to make this process "prettier", but what I have shown here could be done with most modern editors in just a few seconds. It is certainly not something you could do during a session for instant analysis, but is very good information to show to your player after an event. I try to put several plays on a single video so they can thumb through their own work. I love to watch my kids analyze their own work. It's even cooler when they find things you didn't see.
Here's the output of the process I discussed above:
[video=youtube_share;1DU-AHTuvMo]http://youtu.be/1DU-AHTuvMo[/video]