No problem. It's called out in the legislation that anything not explicitly stated as exempt requires planning permission. There are a few situations called out in the exemptions for fencing, but you can see the maximum height of any such fencing to remain as exempted is 2m or 3m for deer fencing.
The laying out of land (i.e. the marking of lines) and the playing of sports on said land is exempt under Class 33(c) so long as no charge is ever applied to the public on entry. The erection of ball catching nets do not fall under this, or other exemptions. You can look up the planning applications for other sports grounds in your vicinity online for the details required to submit such a request.
Where reasonable and the nets won't cause issues for neighbours, there doesn't seem to be any major issues in securing planning.