user31951: I'm studying the Spanish opening by developing some possible attacks against it and seeing how it could resist those attacks.
In the below position, White has moved the light-squared bishop from f1 to b5, after which Black attacked it.
[FEN "rnbqkb1r/3p1ppp/2p2n2/1p2p3/p3P3/1B1P1N2/PPP2PPP/RNBQ1RK1 w Qkq - 0 1"]

I'm struggling with what should be considered an optimal move for the shackled bishop.

user26335: White's best move is to use the Desperado tactic at this point reaching a position where Black is up material but can't castle and is slightly behind in development. There is nothing better for White.
Stockfish 14+ NNUE evaluation is -2.6 (depth = 34, 7450k nodes/s) with best play starting with 1. Bxf7+ to at least snag a pawn for the Bishop and damage the structure around Black's King (source).
The diagram gives the top two lines from the Engine Overlord's perspective.
[FEN "rnbqkb1r/3p1ppp/2p2n2/1p2p3/p3P3/1B1P1N2/PPP2PPP/RNBQ1RK1 w Qkq - 0 1"]

1. Bxf7+ Kxf7 2. Nxe5+ Kg8 3. b3 d6 4. Nf3 h6 5. bxa4 bxa4 6. Re1 Nbd7 7. Nbd2 Ne5 8. d4 Nxf3+
(1. Bxa4 {Stockfish rates this line as -4.6.} bxa4 2. Nxe5 d5 3. c4 dxe4 4. dxe4 Qxd1 5. Rxd1 Be6)

Other moves (e.g., 1. Bxa4, 1. Nxe5, 1. d4, 1. Nc3)  are decidedly worse for White.

user30239: 1 - This is not the Spanish Opening as Black did not play 2...Nc6
It appears to be a rather poor trap in the Open Game by Black against a White player that might be inclined to play the Spanish:

e4   e5
Nf3  a5? { leaving the e5 pawn undefended }
Bb5?    { avoiding to capture the undefended e5 pawn }
...Nf6!?
d3?? c6
Ba4  b5
Bb3  a4

or perhaps from the Petrov's Defense by reversing Nf6 and a5
2 - Either way White should not have played Bb5. Bb5 is not a normal choice in the Petrov's Defense for White. Nxe5 would be better. And Bb5 is simply a tactical mistake after the opponent plays 2...a5.
So the conclusion is to not try and find a way out of this horrible position but to avoid getting in this position. If you decide to play a certain opening, be it the Spanish Opening or whatever, and you don't make your decisions based on your opponent's replies then you will fall for traps. If you are going to play the Spanish Opening, then you should know how to play against the Petrov's Defense and you should be aware of the a5, c6, b5, a6 trap against Bb5. It is a common theme in many openings involving Bb5 and Bf5.

31951: <p>I'm studying the Spanish opening by developing some possible attacks against it and seeing how it could resist those attacks.</p>
<p>In the below position, White has moved the light-squared bishop from f1 to b5, after which Black attacked it.</p>
<pre><code>[FEN &quot;rnbqkb1r/3p1ppp/2p2n2/1p2p3/p3P3/1B1P1N2/PPP2PPP/RNBQ1RK1 w Qkq - 0 1&quot;]
</code></pre>
<p>I'm struggling with what should be considered an <strong>optimal</strong> move for the shackled bishop.</p>
 26335: <p>White's best move is to use the <a href="https://en.wikipedia.org/wiki/Desperado_(chess)" rel="nofollow noreferrer">Desperado tactic</a> at this point reaching a position where Black is up material but can't castle and is slightly behind in development. There is nothing better for White.</p>
<p>Stockfish 14+ NNUE evaluation is -2.6 (depth = 34, 7450k nodes/s) with best play starting with <strong>1. Bxf7+</strong> to at least snag a pawn for the Bishop and damage the structure around Black's King (<a href="https://lichess.org/analysis/standard/rnbqkb1r/3p1ppp/2p2n2/1p2p3/p3P3/1B1P1N2/PPP2PPP/RNBQ1RK1_w_Qkq_-_0_1" rel="nofollow noreferrer">source</a>).</p>
<p>The diagram gives the top two lines from the Engine Overlord's perspective.</p>
<pre><code>[FEN &quot;rnbqkb1r/3p1ppp/2p2n2/1p2p3/p3P3/1B1P1N2/PPP2PPP/RNBQ1RK1 w Qkq - 0 1&quot;]

1. Bxf7+ Kxf7 2. Nxe5+ Kg8 3. b3 d6 4. Nf3 h6 5. bxa4 bxa4 6. Re1 Nbd7 7. Nbd2 Ne5 8. d4 Nxf3+
(1. Bxa4 {Stockfish rates this line as -4.6.} bxa4 2. Nxe5 d5 3. c4 dxe4 4. dxe4 Qxd1 5. Rxd1 Be6)
</code></pre>
<p>Other moves (e.g., 1. Bxa4, 1. Nxe5, 1. d4, 1. Nc3)  are decidedly worse for White.</p>
 30239: <p>1 - This is not the Spanish Opening as Black did not play 2...Nc6</p>
<p>It appears to be a rather poor trap in the Open Game by Black against a White player that might be inclined to play the Spanish:</p>
<ol>
<li>e4   e5</li>
<li>Nf3  a5? { leaving the e5 pawn undefended }</li>
<li>Bb5?    { avoiding to capture the undefended e5 pawn }
...Nf6!?</li>
<li>d3?? c6</li>
<li>Ba4  b5</li>
<li>Bb3  a4</li>
</ol>
<p>or perhaps from the Petrov's Defense by reversing Nf6 and a5</p>
<p>2 - Either way White should not have played Bb5. Bb5 is not a normal choice in the Petrov's Defense for White. Nxe5 would be better. And Bb5 is simply a tactical mistake after the opponent plays 2...a5.</p>
<p>So the conclusion is to not try and find a way out of this horrible position but to avoid getting in this position. If you decide to play a certain opening, be it the Spanish Opening or whatever, and you don't make your decisions based on your opponent's replies then you will fall for traps. If you are going to play the Spanish Opening, then you should know how to play against the Petrov's Defense and you should be aware of the a5, c6, b5, a6 trap against Bb5. It is a common theme in many openings involving Bb5 and Bf5.</p>
