IMPS
1♠ = 5+♠ 11-15 hcp. In 3rd position it could be 10.
Your possible continuations with this passed hand are:
1. Pass then support spades next round. [Range = I'm not sure what hand would take this option. Option 3 is safe with a weak hand and more obstructive.]
2. 1NT forcing asking partner to show strength and any extra length. If you rebid 2♠ you might have only 2-card support. If you rebid 3♠ you would show 3♠ and about 8 hcp.
3. 2♥ which asks partner to bid 2♠ which you will pass. Only with an exceptional hand will partner break the transfer. [Range = any hand you don't think is worth an invite. Could be **very** weak.]
4. 2♠ which shows a constructive 9-10 without a shortage.
Which would you choose?
[Edit: Added ranges for 1 and 3]
[Of course I wouldn't be posting this if there wasn't an unhappy ending.]