In my mobile app (android + ios) you can either choose ALL PLAYERS, or search and choose specific player from the search results (e.g LEBRON JAMES).
Were should I put the ALL PLAYERS option? above the search? as the first option? last option? below? somewhere else?
Edit: added skecth - sizes are not important
download bmml source – Wireframes created with Balsamiq Mockups
Question is , how often do you see users selecting that option "All Players". If its a very frequently used option then put it as the first choice at the top of the list, that is straight forward.
Or as soon as the user enters the search box, before even entering a key, first option (and only) shows up as "Select All Players".. entering a key value will get the search back to how you show in second pic. You might want to still carry the "Select all" option even after any key entry based on your requirement.
Ok, so based on your notes and sketch - attaching a suggestion. This one seems to be a straight-forward one, where you could place the All option as the first one by default as shown.
1) Since it only appears in a sub-section of the search (Players), this makes even more sense.
2) Plus, this is an excepted pattern which many websites/apps use. Something that quickly comes in mind is Amazon's category drop down. See a grab attached.
3) Possibly, you could differentiate that option (All) by a slight visual tone.
It is good practice on iOS to put the "Select All" button in the navigation bar where users can select from multiple list items when a filter / search view is modally presented.
You can use the same behavior on Android as well.
Though answering your question based on your comment that you're still in the design / sketching phase is not great... I'd suggest (as other people already did) that you give some more info for which OS you're designing for and what type of view you want to present.
