RallyIQ

WTA · Left-handed · 6 charted matches · 2022–2026

Kayla Day

Against an average opponent

Serve points won 58.0% ±3.8 raw 57.1% · tour 56.3% · 403 points
Return points won 42.6% ±3.8 raw 41.3% · tour 43.7% · 450 points

Serve and return points won, refitted against every opponent at once so a record built on weak or strong opposition is put on the same scale. Career, all surfaces, with a 90% margin. Raw is the plain share of points won.

Value per 100 shots

Direction choice −0.37 ±0.16 better than 3% of WTA · raw −0.36
Shot selection −0.18 ±0.14 better than 29% of WTA · raw −0.14
Execution +0.97 ±0.91 better than 91% of WTA · raw +1.23
Points left on the table 3.13 per 100 shots vs best direction · lower than 7% of WTA

Points gained per 100 shots compared with an average tour player in the same position, adjusted for the strength of the opponents faced, with a 90% margin (shots clustered by match). Raw is before the opponent adjustment. Built on 2,735 shots.

Shot expected value

The share of points Kayla Day goes on to win after each option in the positions they face most often, shrunk toward tour average when the sample is small. Showing the 8 most-used options; teal marks the best one with at least 30 shots.

Rally, shots 5–8: drive to your backhand side

position worth 45% to the average player · 166 shots

OptionUsedWin %Tour
BH through the middle 49% 38.9%±7.9 43.3%
BH crosscourt 27% 48.5%±10.2 47.6%
BH slice through the middle 10% 27.5%±12.2 34.4%
BH down the line 9% 46.7%±13.9 46.8%

Long rally, 9+: drive to your backhand side

position worth 44% to the average player · 166 shots

OptionUsedWin %Tour
BH crosscourt 43% 56.1%±8.5 47.9%
BH through the middle 35% 34.0%±8.8 42.7%
BH slice through the middle 13% 33.4%±12.1 33.4%

Rally, shots 5–8: drive to your forehand side

position worth 43% to the average player · 157 shots

OptionUsedWin %Tour
FH crosscourt 43% 43.6%±8.7 46.7%
FH through the middle 24% 40.8%±10.7 41.3%
FH down the line 20% 37.2%±11.1 44.9%
FH slice through the middle 8% 32.9%±13.5 29.2%

Long rally, 9+: drive to your forehand side

position worth 44% to the average player · 145 shots

OptionUsedWin %Tour
FH crosscourt 53% 46.8%±8.3 47.0%
FH through the middle 21% 34.6%±11.1 41.5%
FH down the line 12% 46.7%±13.5 46.4%
FH slice through the middle 10% 22.5%±11.6 29.3%

Serve under pressure

Pressure predictability index +20 How much less varied Kayla Day's first-serve direction gets on break points. Positive means easier to read. Based on 42 break-point first serves.

Deuce court

1st serveUsageBreak ptWon when in
Wide 35% 40% 66% / 66%
Body 17% 13% 56% / 57%
T 48% 47% 71% / 68%

202 normal · 15 break-point 1st serves

Ad court

1st serveUsageBreak ptWon when in
Wide 42% 63% ▲ 61% / 66%
Body 29% 4% ▼ 61% / 56%
T 30% 33% 65% / 64%

159 normal · 27 break-point 1st serves

Is the serve mix in equilibrium?

Game theory says a well-mixed server wins equally often with every direction they use. If one direction wins more, it's underused and points are being left behind. This is the minimax test Walker and Wooders ran on Wimbledon finals, applied to every charted first serve. Win rates include faults. "Optimal" allows for returners reading a habit. A direction loses 0.19 points per 100 serves for every 10 points of habitual usage, measured from WTA servers whose mix drifted between matches. Shifts stay within the range servers' habits actually vary, the only range that response was measured over.

Deuce court

1st serveUsagePoints wonOptimal
Wide35% 56.6%±7.9 n=76 50% ▲
Body17% 53.9%±10.0 n=37 2% ▼
T48% 57.1%±7.0 n=104 48%

Consistent with an optimal mix (p = 0.84).
Optimal mix: +0.6 per 100 first serves.

Ad court

1st serveUsagePoints won
Wide45% 56.2%±7.7 n=83
Body25% 60.0%±9.2 n=47
T30% 58.8%±8.7 n=56

Consistent with an optimal mix (p = 0.79).

Exploitability 0.61 points per 100 first serves What the optimal mix would win over the current one, both courts. More exploitable than 100% of WTA servers. Tested on matches they weren't fitted on, WTA mixes picked this way win 0.42 per 100 first serves on average.

Repeating the previous direction to the same court: +6.6±6.8 points per 100 against switching. Negative means returners read repeats. Tour-wide, repeating costs women about 0.4 points per 100 and costs men nothing, so men's returners don't measurably anticipate direction. (136 repeats, 255 switches.)

Return by serve direction

Return points won against each serve direction, compared with the tour average.

ServeCourtDirectionPointsWonvs tour
1stAd courtBody 40 43% −0.8±9.7
1stAd courtT 48 41% +5.1±9.1
1stAd courtWide 59 39% +4.1±8.5
1stDeuce courtBody 66 40% −2.2±8.2
1stDeuce courtT 22 32% −0.1±10.6
1stDeuce courtWide 74 33% −1.1±7.6
2ndAd courtBody 34 48% −7.4±10.3
2ndAd courtT 16 55% +0.4±12.1
2ndAd courtWide 21 51% −2.4±11.5
2ndDeuce courtBody 40 50% −4.0±9.8
2ndDeuce courtT 7 56% +0.2±13.4
2ndDeuce courtWide 22 52% −1.6±11.4

Signature patterns

Recurring sequences that win more than Kayla Day's own baseline, ranked by edge weighted by how often they're used.

Serve → +1

  1. Not enough data

Return

  1. Not enough data

Rally, consecutive own shots

  1. BH through the middle → BH crosscourt used 5.4% · won 54% · +7.9±10.5 vs own baseline
  2. BH crosscourt → BH crosscourt used 5.3% · won 51% · +5.5±10.6 vs own baseline
  3. FH through the middle → BH crosscourt used 4.0% · won 49% · +2.8±11.3 vs own baseline
  4. FH crosscourt → BH through the middle used 6.0% · won 48% · +2.3±10.2 vs own baseline
  5. BH through the middle → BH through the middle used 6.2% · won 47% · +1.5±10.1 vs own baseline

Discovered sequences

Mined from every me → opponent → me run of three shots, with no templates. Ranked by how much more often Kayla Day wins the point once the sequence happens, weighted by how often it happens. Think of them as chess openings.

  1. FH crosscourt → BH through the middle → BH through the middle used 1.6% · won 55% · +11.2±11.9 vs own baseline · +22.1 vs tour on the same sequence Disrupted by Elina Avanesyan (11/17)
  2. BH crosscourt → FH crosscourt → BH crosscourt used 2.4% · won 52% · +7.6±10.8 vs own baseline · +9.4 vs tour on the same sequence Disrupted by Elina Avanesyan (14/24)
  3. BH through the middle → FH crosscourt → BH crosscourt used 1.8% · won 52% · +7.9±11.6 vs own baseline · +11.8 vs tour on the same sequence Disrupted by Elina Avanesyan (10/17)
  4. FH crosscourt → BH through the middle → FH crosscourt used 1.5% · won 48% · +3.8±12.1 vs own baseline · +1.2 vs tour on the same sequence Disrupted by Elina Avanesyan (7/14)
  5. FH crosscourt → BH crosscourt → FH crosscourt used 4.2% · won 46% · +1.7±8.9 vs own baseline · −1.7 vs tour on the same sequence Disrupted by Caroline Dolehide (2/6), Elina Avanesyan (18/40)
  6. FH through the middle → FH crosscourt → BH crosscourt used 1.1% · won 45% · +0.9±13.0 vs own baseline · +0.2 vs tour on the same sequence

Strengths and vulnerabilities

Value per 100 shots compared with the average player hitting (strengths) or facing (vulnerabilities) the same shot. Only shot types seen at least 120 times.

Hurts opponents most with

BH to their forehand · rally+4.4159
FH to their backhand · rally+2.7279
BH to the middle · rally+1.0222
FH to the middle · rally±0.0128

Most exposed to

BH to their forehand · rally−5.7207
FH to their backhand · rally−1.5292
BH to the middle · rally−0.8123
FH to the middle · rally+1.4128
FH to their forehand · rally+2.3160

Active players who are best at the shot in the top weakness: Sara Sorribes Tormo, Alexandra Eala, Caroline Wozniacki, Alize Cornet, Anastasija Sevastova

Charted matches